Yeah, I’m having the same issues with an Apple App Store account, and a Roku, both based on Canadian setups with HBOGo unavailable.
If I log out of one App Store on my iPad, and log into a different Taiwan account, I can get the app and presumably subscribe (and then screen share to my Roku) but I’m not sure if I’d also have to log in and out of different stores to then use it afterwards.
We have no Taiwanese cable at all, so subscribing that way isn’t an option.
Edit to add @jdsmith in: