A first base station is configured to execute instructions of the first BS receiving a first interface message for a communication device from a second BS; the first BS transmitting a second interface message to the second BS in response to the first interface message, wherein the second interface message comprises a secondary cell group configuration and an information element causing the first BS to comprise an indication indicating release of SCG in a radio resource control message; and the first BS transmitting the RRC message to the communication device, wherein the RRC message comprises the SCG configuration and the indication.