Provided are a method by which a first device performs wireless communication, and an apparatus supporting same. The method may comprise the steps of: receiving, from a base station, first downlink control information (DCI) for activating a configured sidelink (SL) grant, wherein the first DCI includes information related to a physical uplink control channel (PUCCH) resource for reporting SL hybrid automatic repeat request (HARD) feedback to the base station; transmitting a medium access control protocol data unit (MAC PDU) to a second device through a physical sidelink shared channel (PSSCH) on the basis of the configured SL grant; receiving, from the base station, second DCI for deactivating the configured SL grant; transmitting, to the base station, an SL confirmation medium access control (MAC) control element (CE) in response to the second DCI; and determining whether the PUCCH resource related to at least one SL resource allocated by the configured SL grant is valid on the basis of the time at which the SL confirmation MAC CE was transmitted.