An apparatus, a method, and a program that contribute to clarifying a behavior of a network and a UE when the USS is not found in the UUAA-SM procedure are provided. An SMF receives from a UE a session establishment request message including an address of a USS and transmits to a UAS-NF an invocation message of an NEF authentication service including the address of the USS. The SMF receives from the UAS-NF a response message and transmit to the UE a reject response message to the session establishment request message when the response message includes a failure cause for the USS corresponding to the address of the USS. The reject response message includes information indicating a failure of a service related to USS corresponding to the address of the USS. This contributes to clarify the behavior of the SMF when the USS is not found in the UUAA-SM procedure.