Been having a massive pain trying to sign up for this as Thai cards simply don't seem to work, and they recently changed my UK account from the sandpit address to my current one, which fucked me using that as well.
On a whim I thought I'd search Lazada and would you believe it but you can get a year of YT Premium (and YT music) for Bt340 a year. You just buy it and they send you an email address and a password. I've had it about a week and it's all fine, so I assume they're using a legal card in a legal territory.