Following the EU guideline you need to apply the VAT % of the users country on the sale.
In order to apply the correct VAT %, the EU says you need to have 2 pieces of non conflicting pieces of evidence that match.
Furthermore: “If you offer telecommunications, broadcasting and electronic services, these services will always be taxed in the country where the customer belongs. For a non-taxable person it is the place where he is established, has a permanent address or usually resides.”
For my matching process I will register:
What do you do if the 3 pieces of evidence do not match?