5G Registration Failure — Metropolitan Region

A customer support ticket has escalated: a European subscriber in a metropolitan area (IMSI 262-01-01234567890) cannot attach to the 5G network. The UE shows "No Service" after a few retries and falls back to LTE. The customer already swapped SIMs and rebooted the phone. 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 UDM (10.45.0.7) SBI traffic is also included so you can correlate the AMF's subscription lookup. 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.