In case anyone else has this issue, I recommend the following, in order to avoid having to get extra help:
Know that google voice has a
consumer and a
business version, so if you are using the regular old google voice that is free with your email (or was) then you need to pay $3 and unlock the number before porting. Using an incognito window for all things google seems to be key in this process. The following information will help you with that:
To unlock a number, do this: use a desktop or laptop computer's web browser, not a phone or tablet. If you're using Google Chrome Browser or Safari, press Ctrl-Shift-N to open an incognito browsing window. IF you're using Firefox, press Ctrl-Shift-P to open a private browsing window.
In that window, sign into the one and only one Google/Gmail account that holds the number you wish to unlock, then go to this page:
https://www.google.com/voice/unlockFor
Business (aka GSuite), you don't need to unlock, but you do need to get the pin. Go to Gsuite - Admin - then to Core Apps - then Voice - then number porting, then look up at the top for the link that says "port out info". Then you will get a pop-up with the PIN. The problem is that the pin numbers are 10 digits and the RingCentral porting form seems to only let you put 8 digits in. So, do yourself a favor and change the pin to 8 digits. The little pencil will let you do that. BUT, it's not instantaneous, so you think it's not changing because it keeps showing you the old one. Just go away for a while and come back. Mine took an hour or so, I think.
Once that's all fixed, go back to your RingCentral form and try the new pin. Then cross your fingers.
Hope people find this helpful. It's frustrating to deal with Google Voice.
