We are having the SAME issue… and TMobile hasn't been able to figure out why yet.  Meanwhile, we are paying for a watch that we can't use.  :(

Same issue here. Cant add my wife to family

group, same error!

Chiming in with the same problem. Just got off the phone with Tmo tech support with no help at all. They told me that on their end my spouse is already added as a guardian. I a.m. able to add her as a guardian, but she won't show up in our family group. What's worse is, if I remove her completely as a guardian and try to re-add her, we get stuck in this setup loop where she won't be able to even open the app dashboard after being re-invited as a guardian. It loops back to the welcome page and a red notification bar at the bottom pops up saying "An error has occurred, please try again later."

We tried un-/re-installing apps on both my phone and her's, restarting, the whole deal. No go.

The tech suggested we take it into a retail store for an in-person troubleshooting, but I don’t have high hopes. 

I did notice a few other threads reporting the same or similar issues, I wonder if tech support looks at this forum.

Yes, exact same thing going on with me, maybe they need to update the app or something…. Please let me know if you get it solved at the store (but like you I doubt that is likely). I hope tmobile tech support reads this as well!

Push the contacts menu on the SyncUP app and create a contact for the person and send the invite through that way and it should work I just figured it out