Thanks for coming back on this. So, if understand the second part of your answer, the reverse charge mechanism applies for your EU VAT registered customers, right?
If that is right, there should be no VAT charged by your side on the sale.
When the Reverse Charge is applied, the recipient of the goods or services makes the declaration of both their purchase (input VAT) and the supplier’s sale (output VAT) in their VAT return. In this way, the two entries cancel each other from a cash payment perspective in the same return.
Anyway, I will not chase this any further. I bet you have a strong finance department over there at Epic. This issue is something my accountants raised, after they tried to book invoices from Marketplace purchases. Based on my accountants view, you shouldn’t charge VAT.