5G Registration Failure — Metropolitan Region

A customer support ticket has escalated: a subscriber of 262-02 (IMSI 262-02-0123456789), at a site with no 262-02 coverage, is camping on 262-01 (national roaming) and cannot register on the 5G network. The phone shows "No Service" on 262-01; the customer has already swapped SIMs and rebooted, and nothing changed. Your team captured the NGAP signalling between the gNB (10.50.0.10) and the AMF (10.45.0.1) while reproducing the issue on the lab bench. The home UDM (10.45.0.7) SBI traffic is also included so you can correlate the AMF's registration with it. On the bench the AMF reaches that UDM directly; across a real roaming border the same request passes through both operators' SEPPs. NAS messages sent after security is switched on (#5 onward) are ciphered on the wire and are shown deciphered here. Your job: open the trace, walk through the registration procedure, identify the 5GMM reject cause (TS 24.501 §9.11.3.2), and decide whether this is a UE-side configuration problem or a core-network/subscription problem that the NOC needs to fix.