In the US it's illegal to print your own currency and use it for commercial purposes. This doesn't preclude the ability to legally exchange goods in a foreign currency because, while there may be a whole lot of potential currencies, it's not that difficult to create an allowlist of approved currencies.

I personally think this is a pretty stupid decision, but iit should be pretty easy to fairly apply so long as the Thai SEC lays out clear guidelines on which currencies are approved.

And, I am avoiding making any sort of comment on whether currencies are worthy of being on that approved list. It's Thailand and the sovereign government has the right to make currency regulation decisions as arbitrarily as it wants.