Hi Manun1213 & DapaminSX,
We have reviewed your form and we can also observe something odd in your form. But when we try to reproduce this by using our own formulas everything is fine.
I am almost sure that it is related to the way you are doing your equations in the form. Please look at https://docs.gravityforms.com/using-calculations/ and make sure that you follow all guidelines there. You can even check that there is something wrong in your calculations if you observe the entries for your form. For example, the entry with ID 18 had an order total of 3.819.541,76 and a totalpriceplusBTW of 620,88.
I would strongly recommend that you rebuild your calculation logic. Don’t use products and quantities if you are only using them as input for your calculation. In those cases, number fields are the way to go.
It would make a lot more sense to use the product fields only for tax and total amount. Then use the gravityforms total field for the amount to be send to Mollie.
Best Regards, Petra