Overleaf compatibility

[jopschilder]

I am trying out this code in overleaf but i am having a problem when using the hours itemization without project. The format of the headers looks to be off with respect to the itemization with project and the "amount" ("Bedrag" in dutch) is displayed below the date instead of "Bedrag".
Furthermore i am trying to calculate more amounts such as the BTW (Dutch VAT) which is 21% of the total, and then to sum the total including BTW but the results only give me 0.00
I would love some help or explanation about these parts.

Thanks in advance!