How to do vat reverse charges in Wave?.
Wave doesn't have features to handle VAT reverse charges, so they aren't currently supported. There's no way to input a negative tax rate in Wave for now.
You might be able to come up with a workaround, but when it comes to situations related to taxes, it's always best to discuss it with an accountant. They know much more than we do about your local regulations, and they'll be able to help you get around this limitation better than we could.
With that said, I'll pass your comment along as feedback to our product team.