ESM cause #66 Requested APN not supported in current RAT and PLMN combination
ESM cause (LTE NAS)3GPP TS 24.301 §9.9.4.4 and Annex B
What it means
Requested APN not supported in current RAT and PLMN combination: e.g. the APN is not allowed over LTE in this visited network.
Where you see it
In LTE NAS PDN connectivity reject, bearer resource reject or EPS bearer deactivation.
What to check
Check the APN's allowed access types and the roaming agreement for it.
Check the GTPv2 Create Session Response and the HSS APN configuration for the same APN.
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