Firefox

https://kycnot.me/search?q=sms&type=

You can use any of these services.

If you want to debug, take the phone number you're getting from relay, and go over to twilio and look up that phone number. See if it's attached to a voip service. Many SMS authentication services simply refuse to send a message to a VoIP number

This is why service providers, like in the directory above, exist to provide non-voip phone number access online.