3GPP 23.501 v20.2.0 — the document's own text

5.17.5.2.1 Interworking with N26 interface

Taught in 19. Living next to 4G (The 5G system architecture, in depth), 7. Roaming, other accesses, the edge and the outside (The 5G system architecture, overview).

In addition to the interworking principles documented in clause 5.17.2.2, the following applies for interworking with N26:

When UE moves from EPS to 5GS, when the AMF registers in UDM, if no event subscription via UDM is available, the AMF indicates the situation to the UDM and in this case the UDM can decide if the event subscriptions should be provisioned, otherwise if the AMF has event subscription information, after the registration procedure is completed, the AMF may inform the UDM of the currently subscribed events and UDM will do synchronization if needed.
When UE moves from 5GS to EPS, the MME gets monitoring event configuration from HSS during as part of mobility procedure as specified in clause 4.11.1.3.2 of TS 23.502 [3].