A method performed by a user equipment, UE, operating in a wireless communication system, the method comprising: transmitting a registration request message to an access and mobility management function, AMF, wherein the registration request message includes requested network slice selection assistance information, NSSAI, including at least one single NSSAI, S-NSSAI, corresponding to a network slice with which the UE intends to register; receiving, from the AMF, a registration accept message in response to the registration request message, wherein, based on the AMF rejecting an S-NSSAI among the at least one S-NSSAI in the requested NSSAI: the registration accept message comprises (i) the rejected S-NSSAI, and (ii) a rejection cause for the rejected S-NSSAI, the rejection cause is at least one of (i) the rejected S-NSSAI being not available in a current public land mobile network, PLMN, or (ii) the rejected S-NSSAI being not available in a current registration area, and the method further comprises: storing the rejected S-NSSAI in a rejected NSSAI list based on the rejection cause; attempting to use the stored rejected S-NSSAI based on (i) the rejection cause being that the stored rejected S-NSSAI is not available in the current registration area, and (ii) the UE leaving the current registration area. transmitting a registration request message to an access and mobility management function, AMF, wherein the registration request message includes requested network slice selection assistance information, NSSAI, including at least one single NSSAI, S-NSSAI, corresponding to a network slice with which the UE intends to register; receiving, from the AMF, a registration accept message in response to the registration request message, wherein, based on the AMF rejecting an S-NSSAI among the at least one S-NSSAI in the requested NSSAI: the registration accept message comprises (i) the rejected S-NSSAI, and (ii) a rejection cause for the rejected S-NSSAI, the rejection cause is at least one of (i) the rejected S-NSSAI being not available in a current public land mobile network, PLMN, or (ii) the rejected S-NSSAI being not available in a current registration area, and the method further comprises: storing the rejected S-NSSAI in a rejected NSSAI list based on the rejection cause; attempting to use the stored rejected S-NSSAI based on (i) the rejection cause being that the stored rejected S-NSSAI is not available in the current registration area, and (ii) the UE leaving the current registration area. the registration accept message comprises (i) the rejected S-NSSAI, and (ii) a rejection cause for the rejected S-NSSAI, the rejection cause is at least one of (i) the rejected S-NSSAI being not available in a current public land mobile network, PLMN, or (ii) the rejected S-NSSAI being not available in a current registration area, and the method further comprises: storing the rejected S-NSSAI in a rejected NSSAI list based on the rejection cause; attempting to use the stored rejected S-NSSAI based on (i) the rejection cause being that the stored rejected S-NSSAI is not available in the current registration area, and (ii) the UE leaving the current registration area. storing the rejected S-NSSAI in a rejected NSSAI list based on the rejection cause; attempting to use the stored rejected S-NSSAI based on (i) the rejection cause being that the stored rejected S-NSSAI is not available in the current registration area, and (ii) the UE leaving the current registration area.