As discussed on discord...
This is what the invoice needs to include:
In all cases
  • Our Vat ID
For Affiliates in Germany
  • Their VAT ID if they have one
  • 19% VAT must be included in one of the two ways:
  1. The original payout amount stays the same and the invoice just shows that his "earning" is 81% of it and 19% are VAT
  2. The original payout amount + 19% VAT is paid out and again its shown on the invoice
So basically as long as VAT is handled on the invoice everything is fine, we don't really care which option you choose
For Affiliates in the EU
  • Amount stays the same, but little notice saying "This invoice is subject to the reverse charge mechanism, if applicable."
For everyone else
Nothing special :)
Maybe that is something you can easily pass to the Wise API. We have never worked with Wise before and therefore we do not know that at the moment.
If you can do that, it would be really amazing and you would be like one of the few systems having that feature, which is basically essential to all EU businesses.