I have tried to buy a new license of GSA SER but Avantage denied giving me a License. They asked me to send ID and proof of Address. I did it but then they just sent an automatic email saying it was not correct without giving explanations.
They are in the german syndrome of too many procedure and at the end of the day, it is useless because they make mistakes on invoices.
Plus, they are so slow to get a license.
Hope you consider other payment gateways like paddle which handle the VAT for you.