diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..b5154bd
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2021 Zeros Developer
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
\ No newline at end of file
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..cf38c7c
--- /dev/null
+++ b/README.md
@@ -0,0 +1,3 @@
+# Tripay Library
+
+For usage examples. See `/examples` directory.
\ No newline at end of file
diff --git a/autoload.php b/autoload.php
new file mode 100644
index 0000000..87699bc
--- /dev/null
+++ b/autoload.php
@@ -0,0 +1,10 @@
+<?php
+
+array_map(function ($class) {
+    return require_once $class;
+}, array_merge(
+    glob(__DIR__.'/src/Constants/*.php'),
+    glob(__DIR__.'/src/Exceptions/*.php'),
+    glob(__DIR__.'/src/Drivers/*.php'),
+    glob(__DIR__.'/src/*.php')
+));
diff --git a/composer.json b/composer.json
new file mode 100644
index 0000000..89419b6
--- /dev/null
+++ b/composer.json
@@ -0,0 +1,39 @@
+{
+    "name": "trijayadigital/tripay-php",
+    "description": "TriPay Payment Library for PHP",
+    "type": "library",
+    "homepage": "https://tripay.co.id",
+    "license": "MIT",
+    "support": {
+        "issues": "https://github.com/trijayadigital/tripay-php/issues",
+        "source": "https://github.com/trijayadigital/tripay-php"
+    },
+    "authors": [
+        {
+            "name": "PT Trijaya Digital Grup",
+            "email": "cs@p-store.net"
+        },
+        {
+            "name": "Suyadi",
+            "email": "suyadi.1992@gmail.com"
+        },
+        {
+            "name": "Zeros Technology",
+            "email": "admin@zeros.co.id"
+        }
+    ],
+    "minimum-stability": "dev",
+    "require": {
+    	"php": ">=5.4.0",
+        "ext-json": "*",
+        "ext-curl": "*"
+    },
+    "autoload": {
+    	"psr-4" : {
+          "Tripay\\": "src"
+        }
+    },
+    "require-dev": {
+    	"phpunit/phpunit": "^7"
+    }
+}
\ No newline at end of file
diff --git a/examples/closed-payment/detail-transaksi.php b/examples/closed-payment/detail-transaksi.php
new file mode 100644
index 0000000..d3e9663
--- /dev/null
+++ b/examples/closed-payment/detail-transaksi.php
@@ -0,0 +1,22 @@
+<?php
+
+require '../../autoload.php';
+
+use Tripay\Constants\Environment;
+use Tripay\Transaction;
+
+$environment = Environment::PRODUCTION;
+
+$apiKey = 'CzAxUSKPk7e5vWxhxz7GpXjHVwlFT2VtslWlxuke';
+$reference = 'T00042MIWYR'; // Didapat setelah menjalankan request transaksi
+
+
+$transaction = (new Transaction($environment))
+    ->apiKey($apiKey)
+
+    ->forClosedPayment();
+
+
+$detail = $transaction->detail($reference);
+
+print_r($detail);
diff --git a/examples/closed-payment/request-transaksi.php b/examples/closed-payment/request-transaksi.php
new file mode 100644
index 0000000..9211247
--- /dev/null
+++ b/examples/closed-payment/request-transaksi.php
@@ -0,0 +1,49 @@
+<?php
+require '../../autoload.php';
+
+use Tripay\Constants\Environment;
+use Tripay\Transaction;
+
+$environment = Environment::PRODUCTION;
+
+$apiKey = 'CzAxUSKPk7e5vWxhxz7GpXjHVwlFT2VtslWlxuke';
+$privateKey = 'uyPNa-5VDDJ-jPoNo-YxnJE-2caD9';
+
+$merchantCode = 'T0004';
+$merchantRef = 'TRX-123456'; // Isi sembarang
+$channelCode = 'BRIVA';
+
+$minutes = 1440; // Waktu kedaluwarsa invoice (dalam menit, default 1440 = 24 jam);
+
+$customerName = 'Asep Balon';
+$customerEmail = 'asep.balon@gmail.com';
+$customerPhone = '0812345667890';
+
+
+
+
+$transaction = (new Transaction($environment))
+    ->apiKey($apiKey)
+    ->privateKey($privateKey)
+    ->merchantCode($merchantCode)
+    ->merchantRef($merchantRef)
+    ->channelCode($channelCode)
+
+    ->expiresAfter($minutes)
+
+    ->customerName($customerName)
+    ->customerEmail($customerEmail)
+    ->customerPhone($customerPhone)
+
+    // ->addItem('Nama Produk', 'Harga Satuan', 'Jumlah', 'Kode SKU')
+    ->addItem('Nama Produk 1', 100000, 2, 'SKU-PRODUK-1')
+    ->addItem('Nama Produk 2', 100000, 6, 'SKU-PRODUK-2')
+    ->addItem('Nama Produk 3', 100000, 3, 'SKU-PRODUK-3')
+    ->addItem('Nama Produk 4', 100000, 1, 'SKU-PRODUK-4')
+
+    ->forClosedPayment();
+
+
+$response = $transaction->process();
+
+print_r($response);
diff --git a/examples/merchant/channel-pembayaran.php b/examples/merchant/channel-pembayaran.php
new file mode 100644
index 0000000..c6d704f
--- /dev/null
+++ b/examples/merchant/channel-pembayaran.php
@@ -0,0 +1,19 @@
+<?php
+
+require '../../autoload.php';
+
+use Tripay\Constants\Environment;
+use Tripay\Merchant;
+
+$environment = Environment::PRODUCTION;
+$apiKey = 'CzAxUSKPk7e5vWxhxz7GpXjHVwlFT2VtslWlxuke';
+
+$merchant = (new Merchant($environment))
+    ->apiKey($apiKey);
+
+    // Jika panggil, hanya akan ditampilkan data sesuai channel code saja
+    // ->channelCode('BRIVA');
+
+$channels = $merchant->channels();
+
+print_r($channels);
diff --git a/examples/merchant/daftar-transaksi.php b/examples/merchant/daftar-transaksi.php
new file mode 100644
index 0000000..3ae939d
--- /dev/null
+++ b/examples/merchant/daftar-transaksi.php
@@ -0,0 +1,20 @@
+<?php
+
+require '../../autoload.php';
+
+use Tripay\Constants\Environment;
+use Tripay\Merchant;
+
+$environment = Environment::PRODUCTION;
+
+$apiKey = 'CzAxUSKPk7e5vWxhxz7GpXjHVwlFT2VtslWlxuke';
+
+$page = 1;
+$per_page = 25;
+
+$merchant = (new Merchant($environment))
+    ->apiKey($apiKey);
+
+$transactions = $merchant->transactions($page, $per_page);
+
+print_r($transactions);
diff --git a/examples/merchant/kalkulator-biaya.php b/examples/merchant/kalkulator-biaya.php
new file mode 100644
index 0000000..ec2c332
--- /dev/null
+++ b/examples/merchant/kalkulator-biaya.php
@@ -0,0 +1,22 @@
+<?php
+
+require '../../autoload.php';
+
+use Tripay\Constants\Environment;
+use Tripay\Merchant;
+
+$environment = Environment::PRODUCTION;
+
+$apiKey = 'CzAxUSKPk7e5vWxhxz7GpXjHVwlFT2VtslWlxuke';
+
+$channelCode = 'BRIVA';
+$amount = 100000;
+
+$merchant = (new Merchant($environment))
+    ->apiKey($apiKey)
+    ->channelCode($channelCode);
+
+
+$calculate = $merchant->calculate($amount);
+
+print_r($calculate);
diff --git a/examples/open-payment/daftar-pembayaran.php b/examples/open-payment/daftar-pembayaran.php
new file mode 100644
index 0000000..c178f5b
--- /dev/null
+++ b/examples/open-payment/daftar-pembayaran.php
@@ -0,0 +1,22 @@
+<?php
+
+require '../../autoload.php';
+
+use Tripay\Constants\Environment;
+use Tripay\Transaction;
+
+$environment = Environment::PRODUCTION;
+
+$apiKey = 'CzAxUSKPk7e5vWxhxz7GpXjHVwlFT2VtslWlxuke';
+$uuid = 'T0001-OP1-7lXjI'; // Didapat setelah menjalankan request transaksi
+
+
+$transaction = (new Transaction($environment))
+    ->apiKey($apiKey)
+
+    ->forOpenPayment();
+
+
+$payments = $transaction->payments($uuid);
+
+print_r($payments);
diff --git a/examples/open-payment/detail-transaksi.php b/examples/open-payment/detail-transaksi.php
new file mode 100644
index 0000000..477b20f
--- /dev/null
+++ b/examples/open-payment/detail-transaksi.php
@@ -0,0 +1,22 @@
+<?php
+
+require '../../autoload.php';
+
+use Tripay\Constants\Environment;
+use Tripay\Transaction;
+
+$environment = Environment::PRODUCTION;
+
+$apiKey = 'CzAxUSKPk7e5vWxhxz7GpXjHVwlFT2VtslWlxuke';
+$uuid = 'T0004-OP2-OK0JP5'; // Didapat setelah menjalankan request transaksi
+
+
+$transaction = (new Transaction($environment))
+    ->apiKey($apiKey)
+
+    ->forOpenPayment();
+
+
+$detail = $transaction->detail($uuid);
+
+print_r($detail);
diff --git a/examples/open-payment/request-transaksi.php b/examples/open-payment/request-transaksi.php
new file mode 100644
index 0000000..6768dd8
--- /dev/null
+++ b/examples/open-payment/request-transaksi.php
@@ -0,0 +1,31 @@
+<?php
+
+require '../../autoload.php';
+
+use Tripay\Constants\Environment;
+use Tripay\Transaction;
+
+$environment = Environment::PRODUCTION;
+
+$apiKey = 'CzAxUSKPk7e5vWxhxz7GpXjHVwlFT2VtslWlxuke';
+$privateKey = 'uyPNa-5VDDJ-jPoNo-YxnJE-2caD9';
+
+$merchantCode = 'T0004';
+$merchantRef = 'TRX-123456'; // Isi sembarang
+$channelCode = 'BRIVAOP';
+
+$customerName = 'Asep Balon';
+
+$transaction = (new Transaction($environment))
+    ->apiKey($apiKey)
+    ->privateKey($privateKey)
+    ->merchantCode($merchantCode)
+    ->channelCode($channelCode)
+    ->merchantRef($merchantRef)
+    ->customerName($customerName)
+
+    ->forOpenPayment();
+
+$response = $transaction->process();
+
+print_r($response);
diff --git a/src/Base.php b/src/Base.php
new file mode 100644
index 0000000..60d4357
--- /dev/null
+++ b/src/Base.php
@@ -0,0 +1,175 @@
+<?php
+
+namespace Tripay;
+
+abstract class Base
+{
+    protected $environment;
+    protected $base;
+
+    protected $apiKey;
+    protected $privateKey;
+
+    protected $channelCode;
+    protected $merchantCode;
+    protected $merchantRef;
+
+    /**
+     * Konstruktor
+     *
+     * @param int $environment
+     */
+    public function __construct($environment)
+    {
+        switch ($environment) {
+            case Constants\Environment::PRODUCTION:
+                $this->base = Constants\Endpoint::BASE_LIVE;
+                break;
+
+            case Constants\Environment::DEVELOPMENT:
+                $this->base = Constants\Endpoint::BASE_SANDBOX;
+                break;
+
+            default:
+                throw new Exceptions\InvalidEndpointException(
+                    'Only Environment::PRODUCTION and Environment::DEVELOPMENT are supported'
+                );
+        }
+
+        $this->environment = $environment;
+    }
+
+    /**
+     * Mengambil instruksi pembayaran dari masing-masing channel.
+     *
+     * @return \stdClass
+     */
+    public function instructions()
+    {
+        $payloads = [
+            'code' => $this->channelCode,
+        ];
+
+        return $this->sendRequest('payment/instruction', $payloads);
+    }
+
+    /**
+     * Set api key.
+     *
+     * @param string $apiKey
+     *
+     * @return Merchant
+     */
+    public function apiKey($apiKey)
+    {
+        $this->apiKey = (string) $apiKey;
+
+        return $this;
+    }
+
+    /**
+     * Set private key.
+     *
+     * @param string $privateKey
+     *
+     * @return Merchant
+     */
+    public function privateKey($privateKey)
+    {
+        $this->privateKey = (string) $privateKey;
+
+        return $this;
+    }
+
+    /**
+     * Set payment channel.
+     *
+     * @param string $channelCode
+     *
+     * @return Merchant
+     */
+    public function channelCode($channelCode)
+    {
+        $this->channelCode = (string) $channelCode;
+
+        return $this;
+    }
+
+    /**
+     * Set merchant code.
+     *
+     * @param string $merchantCode
+     *
+     * @return Merchant
+     */
+    public function merchantCode($merchantCode)
+    {
+        $this->merchantCode = (string) $merchantCode;
+
+        return $this;
+    }
+
+    /**
+     * Set reference code.
+     *
+     * @param string $merchantRef
+     *
+     * @return Merchant
+     */
+    public function merchantRef($merchantRef)
+    {
+        $this->merchantRef = (string) $merchantRef;
+
+        return $this;
+    }
+
+    /**
+     * Kirim request.
+     *
+     * @param string $uri
+     * @param array  $payloads
+     *
+     * @return \stdClass
+     */
+
+    protected function request($method, $uri, array $payloads)
+    {
+        $method = (string) $method;
+        $uri = $this->base.$uri;
+
+        // TODO: gunakan socket jika cURL tidak tersedia di server.
+        $driver = new Drivers\Curl();
+        $options = [
+            CURLOPT_HEADER => false,
+            CURLOPT_HTTPHEADER => ['Authorization: Bearer '.$this->apiKey],
+            CURLOPT_FAILONERROR => false,
+        ];
+
+        // if (extension_loaded('curl') && is_callable('curl_init')) {
+        //     $driver = new Drivers\Curl();
+        //     $options = [
+        //         CURLOPT_HEADER => false,
+        //         CURLOPT_HTTPHEADER => ['Authorization: Bearer '.$this->apiKey],
+        //         CURLOPT_FAILONERROR => false,
+        //     ];
+        // } elseif (function_exists('stream_context_create') && is_callable('stream_context_create')) {
+        //     $driver = new Drivers\Stream();
+        //     $options = [
+        //         // ..
+        //     ];
+        // } else {
+        //     throw new \RuntimeException(
+        //         'Please enable curl or stream context before using this library.'
+        //     );
+        // }
+
+        if (! in_array($method, ['get', 'post', 'put', 'delete'])) {
+            throw new Exceptions\InvalidRequestTypeException(sprintf(
+                'Only GET, POST, PUT and DELETE request are currently suported. Got: %s',
+                $this->requestType
+            ));
+        }
+
+        return $driver->request($method, $uri, $payloads, $options);
+    }
+}
diff --git a/src/Constants/Endpoint.php b/src/Constants/Endpoint.php
new file mode 100644
index 0000000..ad1e039
--- /dev/null
+++ b/src/Constants/Endpoint.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace Tripay\Constants;
+
+class Endpoint
+{
+    const BASE_SANDBOX = 'https://tripay.co.id/api-sandbox/';
+    const BASE_LIVE = 'https://tripay.co.id/api/';
+
+    // const BASE_SANDBOX = 'https://tripay-payment.test/api-sandbox/';
+    // const BASE_LIVE = 'https://tripay-payment.test/api/';
+}
diff --git a/src/Constants/Environment.php b/src/Constants/Environment.php
new file mode 100644
index 0000000..ad65307
--- /dev/null
+++ b/src/Constants/Environment.php
@@ -0,0 +1,9 @@
+<?php
+
+namespace Tripay\Constants;
+
+class Environment
+{
+    const PRODUCTION = 'PRODUCTION';
+    const DEVELOPMENT = 'DEVELOPMENT';
+}
diff --git a/src/Drivers/Base.php b/src/Drivers/Base.php
new file mode 100644
index 0000000..dad6897
--- /dev/null
+++ b/src/Drivers/Base.php
@@ -0,0 +1,73 @@
+<?php
+
+namespace Tripay\Drivers;
+
+abstract class Base
+{
+    public function __construct()
+    {
+        // ..
+    }
+
+    /**
+     * Kirim request.
+     *
+     * @param string $method
+     * @param string $url
+     * @param array  $params
+     * @param array  $options
+     *
+     * @return \stdClass
+     */
+    abstract public function request($method, $url, array $params = [], array $options = []);
+
+    /**
+     * Buat user-agent palsu.
+     * Beberapa situs seperti github mewajibkan string user-agent.
+     *
+     * @return string
+     */
+    public function agent()
+    {
+        $year = (int) gmdate('Y');
+        $year = ($year < 2020) ? 2020 : $year;
+        $version = 77 + ($year - 2020) + 2;
+
+        $agents = [
+            'Windows' => 'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:[v].0) Gecko/20100101 Firefox/[v].0',
+            'Linux' => 'Mozilla/5.0 (Linux x86_64; rv:[v].0) Gecko/20100101 Firefox/[v].0',
+            'Darwin' => 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:[v].0) Gecko/20100101 Firefox/[v].0',
+            'BSD' => 'Mozilla/5.0 (X11; FreeBSD amd64; rv:[v].0) Gecko/20100101 Firefox/[v].0',
+            'Solaris' => 'Mozilla/5.0 (Solaris; Solaris x86_64; rv:[v].0) Gecko/20100101 Firefox/[v].0',
+        ];
+
+        $platform = $this->platform();
+        $platform = $platform === 'Unknown' ? 'Linux' : $platform;
+
+        return str_replace('[v]', $version, $agents[$platform]);
+    }
+
+    /**
+     * Ambil sistem operasi server.
+     *
+     * @return string
+     */
+    public function platform()
+    {
+        if ('\\' === DIRECTORY_SEPARATOR) {
+            return 'Windows';
+        }
+
+        $platforms = [
+            'Darwin' => 'Darwin',
+            'DragonFly' => 'BSD',
+            'FreeBSD' => 'BSD',
+            'NetBSD' => 'BSD',
+            'OpenBSD' => 'BSD',
+            'Linux' => 'Linux',
+            'SunOS' => 'Solaris',
+        ];
+
+        return isset($platforms[PHP_OS]) ? $platforms[PHP_OS] : 'Unknown';
+    }
+}
diff --git a/src/Drivers/Curl.php b/src/Drivers/Curl.php
new file mode 100644
index 0000000..e8cf364
--- /dev/null
+++ b/src/Drivers/Curl.php
@@ -0,0 +1,122 @@
+<?php
+
+namespace Tripay\Drivers;
+
+use InvalidArgumentException;
+use Exception;
+
+class Curl extends Base
+{
+    /**
+     * Konstruktor
+     */
+    public function __construct()
+    {
+        parent::__construct();
+    }
+
+    /**
+     * Kirim request.
+     *
+     * @param string $method
+     * @param string $url
+     * @param array  $params
+     * @param array  $options
+     *
+     * @return \stdClass
+     */
+    public function request($method, $url, array $params = [], array $options = [])
+    {
+        $curl = curl_init();
+
+        curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, 0);
+        curl_setopt($curl, CURLOPT_AUTOREFERER, 1);
+        curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
+        curl_setopt($curl, CURLOPT_USERAGENT, $this->agent());
+
+        $query = empty($params) ? null : http_build_query($params, '', '&', PHP_QUERY_RFC1738);
+
+        switch (strtolower($method)) {
+            case 'get':
+                $url .= $query ? '?'.$query : '';
+                curl_setopt($curl, CURLOPT_HTTPGET, 1);
+                break;
+
+            case 'post':
+                if ($query) {
+                    curl_setopt($curl, CURLOPT_POSTFIELDS, $query);
+                }
+
+                if (isset($options[CURLOPT_HTTPHEADER]) && is_array($options[CURLOPT_HTTPHEADER])) {
+                    $options[CURLOPT_HTTPHEADER] = array_merge(
+                        $options[CURLOPT_HTTPHEADER],
+                        ['Content-Type: application/x-www-form-urlencoded']
+                    );
+                } else {
+                    $options[CURLOPT_HTTPHEADER] = ['Content-Type: application/x-www-form-urlencoded'];
+                }
+
+                curl_setopt($curl, CURLOPT_POST, 1);
+                break;
+
+            case 'put':
+                if ($query) {
+                    curl_setopt($curl, CURLOPT_POSTFIELDS, $query);
+                }
+
+                if (isset($options[CURLOPT_HTTPHEADER]) && is_array($options[CURLOPT_HTTPHEADER])) {
+                    $options[CURLOPT_HTTPHEADER] = array_merge(
+                        $options[CURLOPT_HTTPHEADER],
+                        ['Content-Type: application/x-www-form-urlencoded']
+                    );
+                } else {
+                    $options[CURLOPT_HTTPHEADER] = ['Content-Type: application/x-www-form-urlencoded'];
+                }
+
+                curl_setopt($curl, CURLOPT_CUSTOMREQUEST, 'PUT');
+                break;
+
+            case 'delete':
+                if ($query) {
+                    curl_setopt($curl, CURLOPT_POSTFIELDS, $query);
+                }
+
+                if (isset($options[CURLOPT_HTTPHEADER]) && is_array($options[CURLOPT_HTTPHEADER])) {
+                    $options[CURLOPT_HTTPHEADER] = array_merge(
+                        $options[CURLOPT_HTTPHEADER],
+                        ['Content-Type: application/x-www-form-urlencoded']
+                    );
+                } else {
+                    $options[CURLOPT_HTTPHEADER] = ['Content-Type: application/x-www-form-urlencoded'];
+                }
+
+                curl_setopt($curl, CURLOPT_CUSTOMREQUEST, 'DELETE');
+                break;
+
+            default: throw new InvalidArgumentException(sprintf(
+                'Usupported request method: %s',
+                strtoupper($method)
+            ));
+        }
+
+        if (is_array($options) && ! empty($options)) {
+            curl_setopt_array($curl, $options);
+        }
+
+        curl_setopt($curl, CURLOPT_URL, $url);
+
+        $response = curl_exec($curl);
+
+        if (false === $response) {
+            $code = curl_errno($curl);
+            $message = curl_error($curl);
+            curl_close($curl);
+
+            throw new \Exception($message, $code);
+        }
+
+        curl_close($curl);
+
+        return json_decode($response);
+    }
+}
diff --git a/src/Drivers/Stream.php b/src/Drivers/Stream.php
new file mode 100644
index 0000000..23c5083
--- /dev/null
+++ b/src/Drivers/Stream.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Tripay\Drivers;
+
+use InvalidArgumentException;
+use Exception;
+
+class Stream extends Base
+{
+    /**
+     * Konstruktor.
+     */
+    public function __construct()
+    {
+        parent::__construct();
+    }
+
+    /**
+     * Jalankan request.
+     *
+     * @param string $method
+     * @param string $url
+     * @param array  $params
+     * @param array  $options
+     *
+     * @return \stdClass
+     */
+    public function request($method, $url, array $params = [], array $options = [])
+    {
+        // TODO: implementasikan koneksi via stream socket.
+    }
+}
diff --git a/src/Exceptions/DefaultTripayException.php b/src/Exceptions/DefaultTripayException.php
new file mode 100644
index 0000000..bc593f8
--- /dev/null
+++ b/src/Exceptions/DefaultTripayException.php
@@ -0,0 +1,14 @@
+<?php
+
+namespace Tripay\Exceptions;
+
+class DefaultTripayException extends \Exception
+{
+    public function getMessageAsJson()
+    {
+        return json_encode([
+            'success' => false,
+            'message' => $this->getMessage(),
+        ]);
+    }
+}
diff --git a/src/Exceptions/InvalidEndpointException.php b/src/Exceptions/InvalidEndpointException.php
new file mode 100644
index 0000000..8ded2aa
--- /dev/null
+++ b/src/Exceptions/InvalidEndpointException.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Tripay\Exceptions;
+
+class InvalidEndpointException extends DefaultTripayException
+{
+    // ..
+}
diff --git a/src/Exceptions/InvalidRequestTypeException.php b/src/Exceptions/InvalidRequestTypeException.php
new file mode 100644
index 0000000..b1be306
--- /dev/null
+++ b/src/Exceptions/InvalidRequestTypeException.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Tripay\Exceptions;
+
+class InvalidRequestTypeException extends DefaultTripayException
+{
+    // ..
+}
diff --git a/src/Exceptions/InvalidReturnUrlException.php b/src/Exceptions/InvalidReturnUrlException.php
new file mode 100644
index 0000000..0cb3c3e
--- /dev/null
+++ b/src/Exceptions/InvalidReturnUrlException.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Tripay\Exceptions;
+
+class InvalidReturnUrlException extends DefaultTripayException
+{
+    // ..
+}
diff --git a/src/Exceptions/InvalidTransactionTypeException.php b/src/Exceptions/InvalidTransactionTypeException.php
new file mode 100644
index 0000000..88020a6
--- /dev/null
+++ b/src/Exceptions/InvalidTransactionTypeException.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Tripay\Exceptions;
+
+class InvalidTransactionTypeException extends DefaultTripayException
+{
+    // ..
+}
diff --git a/src/Exceptions/InvalidTransactionUuidException.php b/src/Exceptions/InvalidTransactionUuidException.php
new file mode 100644
index 0000000..e8e0fe4
--- /dev/null
+++ b/src/Exceptions/InvalidTransactionUuidException.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Tripay\Exceptions;
+
+class InvalidTransactionUuidException extends DefaultTripayException
+{
+    // ..
+}
diff --git a/src/Merchant.php b/src/Merchant.php
new file mode 100644
index 0000000..94575b1
--- /dev/null
+++ b/src/Merchant.php
@@ -0,0 +1,82 @@
+<?php
+
+namespace Tripay;
+
+class Merchant extends Base
+{
+    /**
+     * Konstruktor.
+     *
+     * @param int $environment
+     */
+    public function __construct($environment)
+    {
+        parent::__construct($environment);
+    }
+
+    /**
+     * Mengambil instruksi pembayaran dari masing-masing channel.
+     *
+     * @return \stdClass
+     */
+    public function instructions()
+    {
+        $payloads = [
+            'code' => $this->channelCode,
+        ];
+
+        return $this->request('get', 'payment/instruction', $payloads);
+    }
+
+    /**
+     * Mendapatkan daftar channel pembayaran yang aktif pada akun merchant anda
+     * beserta informasi lengkap termasuk biaya transaksi dari masing-masing channel.
+     *
+     * @return \stdClass
+     */
+    public function channels()
+    {
+        $payloads = [
+            'code' => $this->channelCode,
+        ];
+
+        return $this->request('get', 'merchant/payment-channel', $payloads);
+    }
+
+    /**
+     * Mendapatkan rincian perhitungan biaya transaksi untuk masing-masing channel
+     * berdasarkan nominal yang ditentukan.
+     *
+     * @param int $price
+     *
+     * @return \stdClass
+     */
+    public function calculate($price)
+    {
+        $payloads = [
+            'code' => $this->channelCode,
+            'amount' => (int) $price,
+        ];
+
+        return $this->request('get', 'merchant/fee-calculator', $payloads);
+    }
+
+    /**
+     * Mendapatkan daftar transaksi merchant.
+     *
+     * @param int $page
+     * @param int $per_page
+     *
+     * @return \stdClass
+     */
+    public function transactions($page = 1, $per_page = 25)
+    {
+        $payloads = [
+            'code' => $this->channelCode,
+            'page' => (int) $page,
+            'per_page' => (int) $per_page,
+        ];
+
+        return $this->request('get', 'merchant/transactions', $payloads);
+    }
+}
diff --git a/src/Transaction.php b/src/Transaction.php
new file mode 100644
index 0000000..872d523
--- /dev/null
+++ b/src/Transaction.php
@@ -0,0 +1,247 @@
+<?php
+
+namespace Tripay;
+
+class Transaction extends Base
+{
+    private $transactionType;
+    private $returnUrl;
+
+    private $customerName;
+    private $customerEmail;
+    private $customerPhone;
+
+    private $expiresAfter;
+    private $items = [];
+
+    /**
+     * Konstruktor.
+     *
+     * @param int $environment
+     */
+    public function __construct($environment)
+    {
+        // default expiry: 24 hours.
+        $this->expiresAfter = $this->expiresAfter(1440);
+
+        parent::__construct($environment);
+    }
+
+    /**
+     * Set operasi untuk open payment.
+     *
+     * @return Transaction
+     */
+    public function forOpenPayment()
+    {
+        $this->transactionType = 'open';
+
+        return $this;
+    }
+
+    /**
+     * Set operasi untuk closed payment.
+     *
+     * @return Transaction
+     */
+    public function forClosedPayment()
+    {
+        $this->transactionType = 'closed';
+
+        return $this;
+    }
+
+    /**
+     * Tambahakan item ke list request.
+     *
+     * @param string $name
+     * @param int    $price
+     * @param int    $quantity
+     * @param string $sku
+     *
+     * @return Transaction
+     */
+    public function addItem($name, $price, $quantity, $sku = null)
+    {
+        $this->items[] = [
+            'sku' => (string) $sku,
+            'name' => (string) $name,
+            'price' => (int) $price,
+            'quantity' => (int) $quantity,
+        ];
+
+        return $this;
+    }
+
+    /**
+     * Set nama customer.
+     *
+     * @param string $name
+     *
+     * @return Transaction
+     */
+    public function customerName($name)
+    {
+        $this->customerName = (string) $name;
+
+        return $this;
+    }
+
+
+
+    /**
+     * Set email customer.
+     *
+     * @param string $email
+     *
+     * @return Transaction
+     */
+    public function customerEmail($email)
+    {
+        $this->customerEmail = (string) $email;
+
+        return $this;
+    }
+
+    /**
+     * Set nomor telepon customer.
+     *
+     * @param string $phone
+     *
+     * @return Transaction
+     */
+    public function customerPhone($phone)
+    {
+        $this->customerPhone = (string) $phone;
+
+        return $this;
+    }
+
+    /**
+     * Set return URL.
+     *
+     * @param string $url
+     *
+     * @return Transaction
+     */
+    public function returnUrl($url)
+    {
+        if (! filter_var($url, FILTER_VALIDATE_URL)) {
+            throw new Exceptions\InvalidRedirectException(sprintf('Invalid URL fornat: %s', $url));
+        }
+
+        $this->returnUrl = $url;
+
+        return $this;
+    }
+
+    /**
+     * Set waktu kedaluwarsa invoice (dalam menit).
+     *
+     * @param int $minutes
+     *
+     * @return Transaction
+     */
+    public function expiresAfter($minutes)
+    {
+        $this->expiresAfter = time() + ((int) $minutes * 60);
+
+        return $this;
+    }
+
+    /**
+     * Proses data transaksi.
+     *
+     * @return \stdClass
+     */
+    public function process()
+    {
+        switch ($this->transactionType) {
+            case 'open':
+                $signature = hash_hmac(
+                    'sha256',
+                    $this->merchantCode.$this->channelCode.$this->merchantRef,
+                    $this->privateKey
+                );
+
+                $payloads = [
+                    'method' => $this->channelCode,
+                    'merchant_ref' => $this->merchantRef,
+                    'customer_name' => $this->customerName,
+                    'signature' => $signature,
+                ];
+
+                return $this->request('post', 'open-payment/create', $payloads);
+
+            case 'closed':
+                $amount = 0;
+
+                for ($i = 0; $i < count($this->items); $i++) {
+                    $amount += (int) $this->items[$i]['price'] * (int) $this->items[$i]['quantity'];
+                }
+
+                $signature = hash_hmac(
+                    'sha256',
+                    $this->merchantCode.$this->merchantRef.$amount,
+                    $this->privateKey
+                );
+
+                $payloads = [
+                    'method' => $this->channelCode,
+                    'merchant_ref' => $this->merchantRef,
+                    'amount' => $amount,
+                    'customer_name' => $this->customerName,
+                    'customer_email' => $this->customerEmail,
+                    'customer_phone' => $this->customerPhone,
+                    'order_items' => $this->items,
+                    'return_url' => $this->returnUrl,
+                    'expired_time' => $this->expiresAfter,
+                    'signature' => $signature,
+                ];
+
+                return $this->request('post', 'transaction/create', $payloads);
+
+            default:
+                throw new Exceptions\InvalidTransactionTypeException(sprintf(
+                    'Only OPEN and CLOSED transaction are supported, got: %s',
+                    $this->transactionType
+                ));
+        }
+    }
+
+
+    public function detail($uuid)
+    {
+        if (! is_string($uuid) || strlen(trim($uuid)) <= 0) {
+            throw new Exceptions\InvalidTransactionUuidException('Transaction UUID should be a non empty string.');
+        }
+
+        switch ($this->transactionType) {
+            case 'open':
+                $payloads = [];
+                return $this->request('get', 'open-payment/'.$uuid.'/detail', $payloads);
+
+            case 'closed':
+                $payloads = ['reference' => $uuid]; // TODO: apakah reference sama dengan uuid?
+                return $this->request('get', 'transaction/detail', $payloads);
+
+            default: throw new Exceptions\InvalidTransactionTypeException(sprintf(
+                'Only OPEN and CLOSED transaction types are supported, got: %s',
+                $this->transactionType
+            ));
+
+        }
+    }
+
+
+    public function payments($uuid)
+    {
+        if (! is_string($uuid) || strlen(trim($uuid)) <= 0) {
+            throw new Exceptions\InvalidTransactionUuidException('Transaction UUID should be a non-empty string.');
+        }
+
+        $payloads = [];
+
+        return $this->request('get', 'open-payment/'.$uuid.'/transactions', $payloads);
+    }
+}