What are /r/Gameflip's favorite Products & Services?

From 3.5 billion Reddit comments

It has to be a regular mobile number. The Internet/VoIP numbers are usually disposable, and some scammers reuse them to make duplicate accounts.

You could ask a close relative to use their mobile number to register, and then enable 2-factor on the Android or iOS app so you can get the login code from there instead of a text message.

If you were using the website to connect Steam, did you see the Steam login popup? You were able to sign in through Steam, and the popup closes, but you got the "can't connect" message on Gameflip? Have you already connected that Steam account to another Gameflip account?

You can also retry that feature on the Android or iOS app.