A method and apparatus for triggering solving mismatch between sidelink BSR and available sidelink transmission in a wireless communication system are disclosed. In one embodiment, the method includes a relay UE establishing a first layer-2 link and a second layer-2 link between the relay UE and a remote UE, wherein the first layer-2 link and the second layer-2 link have two different source identities and a same destination identity. The method further includes the relay UE receiving a sidelink grant from an eNB. The method further includes the relay UE using the sidelink grant to serve the first layer-2 link and the second layer-2 link.