Sites that require phone number verification often block numbers allocated for VoIP services for fear of spammers. YMMV if you've tethered your GV number to a physical device at some point.

I've run into this semi-frequently over the years, and it's always extremely frustrating when it happens, but somehow I can't remember exactly where either.

Old references online point to Facebook, Line, and Snapchat: https://www.reddit.com/r/Googlevoice/comments/3uv3mt/google_...