Since OP said the country isn't in the location list, that's probably the real blocker, not the number. When a platform's signup flow doesn't list your country, the SMS route for that country code is often just not enabled, so retrying with the same SIM won't change anything.
A few things that haven't been mentioned yet:
- Try the signup in the official mobile app instead of the web page (or the other way round). They sometimes use different verification flows.
- Look for a voice-call code option or a "send an SMS to us" option. Some Chinese platforms offer one of these when inbound SMS fails.
- After many failed attempts the number can get rate-limited, so give it a break, ideally a day or so, before trying again.
- Make sure your SIM can receive international SMS. Some prepaid plans block foreign senders by default.
@Koma, which site are you verifying, and with what kind of number? The fix depends a lot on that.