I have a SM-G955N with a custom ROM on T-Mobile that I had been using for years, no updates anywhere near recently but I start getting the “Not Registered on Network” error a week and a half ago. So after a little research I figured it was a firmware thing, I finally got around to flashing a new ROM tonight and the process went well, but I still have the same error as well as “SIM not Provisioned for Voice”
I was completely blindsided by this issue and as a novice that just follows the instructions closely I am unsure what to do. I have made APN edits found in other posts, cleared SIM cache/data and tried re-seating the SIM multiple times. I’m at the end of my rope and don’t even see how this randomly started in the first place, any advice would be appreciated.