For a customer we've got an custom made checkouthandler for afterpay.
The handler works just fine, but the customer wants to charge an paymentfee of 1,99 euros when customer us this method. As soon as we enable this we're getting a vague error saying "field.invalid". I can't figure out where the error is coming from and we don't have access to the source code, so unfortunately debugging is quite difficult.
Will it be an option to add a paymentfee programatically with a FeeProvider or OrderTemplateExtender so that it's added as an additional orderline?
I've also attached the dll. file i'm currently using.