A feature that allows users in the U.S. to participate in GroupMe chats via standard text messages, without needing the app or internet access.
Hi!
Welcome to the Microsoft Q&A forum.
Based from your provided information including the screenshots I do not see anything wrong, I can see that number code is correct, the hyphen is normal to be there and your number would be fine as well.
I have gathered data and shows similar reports of login issues via GroupMe. You can check this link as reference: https://support.microsoft.com/en-us/GroupMe/how-do-i-sign-up-for-groupme?