In Wise use "Funds for long term stay in Thailand" as the reason for the transfer. The code on the Thai bank side depends on the bank: Kasikorn labels it as FT (foreign transfer), no idea about the other banks.
That contradicts previous (recent) reports stating that you have to go through passport control first (at zone 2 preferably) and then head to the re-entry office in the corner on your left. Anyway, I'll see it tomorrow 😁