Hi Tienbao,
	To exit from the game, B can send leaveRoom request. When B calls leaveRoom and A has subscribed the room, A will receive onUserLeftRoom notification.
	If your still getting issue, please check the following steps to troubleshoot:
	A: Creates Room
	A: Joins room
	A: Subscribes Room
	B: Joins room
	B: Subscribes Room
	Also confirm that listeners are added and callbacks are defined.
	B will  be removed from room if B has
	-called leaveRoom API
	-called disconnect API
	-lost the internet connection
	Note:- If you are connection resiliency feature then in third case B will be alive till recovery time is elapsed.
	Let us know if you are still facing problems.