In the present disclosure, a transmitting device transmits a first message comprising i) a first random access preamble with a first random access preamble identifier (RAPID) and ii) a first uplink payload; receives a random access response (RAR) medium access control (MAC) protocol data unit (PDU) including i) a first field set to represent presence of one or more RAPIDs and ii) the one or more RAPIDs; determines whether both of the first RAP and the first payload is successfully transmitted, based on whether the one or more RAPIDs include the first RAPID; and monitors a second message related to the first message based on determining that both of the first RAP and the first payload is successfully transmitted.