I just dropped my AT&T postpaid Unlimited Elite iphone sim into my MT 5G. and it came up with no issues. (8.2.0). so it isn’t a blanket hardware issue… You may need them to check if they have blacklisted your particular IMEI or locked your sim for some reason.
The IMEI mapping is often going to be odd for newer hardware. and the Transit 5G may be in a special place.
See the reponse about:Please copy this message, with the S/N of your device, and email it to [email protected].
We will follow up with you via email.
The modem in question for the -5BD and all of those use the Thales (previously Gemalto) MV31-W M2 card. Until final approval and ownership is sent from Peplink to all of the providers, the IMEI will list the main manufacturer. Only after peplink tells AT&T (or the master IMEI database, I’m not sure how that is coordinated) that a particular MV31-1 module went into a MAX-TST-5GD-T-PRM or a EXM-MINI-15GD can the end database be complete…