A method of handling insufficient resources in a user equipment (UE) during a PDU session establishment procedure is proposed. During a PDU session establishment procedure, UE sends a PDU SESSION ESTABLISHMENT REQUEST message to the network. UE then receives a PDU SESSION ESTABLISHMENT ACCEPT message from the network, the ACCEPT message carries various PDU session parameters including authorized QoS rules and QoS flows. If UE decides to reject the addition of the new authorized QoS flow description or the new authorized QoS rule due to lack of resources, UE may initiate a PDU session release procedure with 5G session management (5GSM) cause IE #26 “insufficient resources”. In an alternative embodiment, UE may synchronize with the network by sending a PDU session modification request message to delete certain QoS rules/flow descriptions with 5GSM cause IE #26 “insufficient resources”.