Question: Which NF can request the NSACF to update the number of UEs registered with a network slice?
Option 1: SMF
Option 2: AMF
Option 3: UE
Option 4: VPLMN Primary (or Central) NSACF
Explanation: The AMF, as the consumer NF, can request the NSACF to update the number of UEs registered with a network slice. This is because the AMF is responsible for managing the registration of UEs with the network and needs to ensure that the number of registered UEs does not exceed the maximum allowed per network slice.