EMM cause (LTE NAS)3GPP TS 24.301 §9.9.3.9 and Annex A
What it means
PLMN not allowed: the subscriber may not use this network at all. The phone puts the PLMN on its forbidden list and won't try it again until restarted.
Where you see it
In LTE NAS Attach reject, Tracking area update reject, Service reject or Detach request.
What to check
Check the roaming agreement and steering/roaming restrictions for this home/visited pair.
Look at the S6a (MME↔HSS) and S11 messages just before the reject: they usually show the real trigger.
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