Wanting to buy Boku Inc (LON:BOKU)

I tried to buy Boku Inc (LON:BOKU) for the UK Portfolio, but my platform provider would not allow me to because it is a "category 3" restricted security. This means that Boku has decided US citizens cannot own the stock and the platform provider doesn't know who is a US citizen so just bans anyone from trading it. Very frustrating given neither me, nor the beneficiary of the account is a US citizen.

Boku looks like a great business too, with a stellar customer list, 90%+ gross margins, huge operating leverage, growing rapidly and at an inflection point. The price is reasonable and management have been buying on market.