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5GS – General Registration – 15 of 24
Signalling flow for TS 23.502 General Register - AMF-UDM

Step 14a-b, verbatim
If the AMF has changed since the last Registration procedure, or if the UE provides a SUPI which doesn't refer to a valid context in the AMF, or if the UE registers to the same AMF it has already registered to a non-3GPP access (i.e. the UE is registered over a non-3GPP access and initiates this Registration procedure to add a 3GPP access), the new AMF registers with the UDM using Nudm_UECM_Registration and subscribes to be notified when the UDM deregisters this AMF. The UDM stores the AMF identity associated to the Access Type and does not remove the AMF identity associated to the other Access Type. UDM may store information provided at registration in UDR, by Nudr_UDM_Update.
AMF retrieves the Access and Mobility subscription data and SMF Selection Subscription data using Nudm_SDM_Get. This requires that UDM may retrieve this information from UDR by Nudr_UDM_Query(Access and Mobility Subscription data). After a successful response is received, the AMF subscribes to be notified using Nudm_SDM_Subscribe when the data requested is modified, UDM may subscribe to UDR by Nudr_UDM_Subscribe. The GPSI is provided to the AMF in the subscription data from the UDM if the GPSI is available in the UE subscription data.
The new AMF provides the Access Type it serves for the UE to the UDM and the Access Type is set to "3GPP access". The UDM stores the associated Access Type together with the serving AMF in UDR by Nudr_UDM_Update.
The new AMF creates an MM context for the UE after getting the mobility subscription data from the UDM.
For an Emergency Registration in which the UE was not successfully authenticated, the AMF shall not register with the UDM.
For an Emergency Registration, the AMF shall not check for access restrictions, regional restrictions or subscription restrictions. For an Emergency Registration, the AMF shall ignore any unsuccessful registration response from UDM and continue with the Registration procedure.