In WCS-iOS-SDK-2.5.2/Headers/FPWCSApi2RoomManager.h
Objective-C:
// Wrong
- (FPWCSApi2Room *)on:(kFPWCSRoomManagerEvent)event
callback:(RoomManagerEventCallback)callback;
// It should be
- (FPWCSApi2RoomManager *)on:(kFPWCSRoomManagerEvent)event
callback:(RoomManagerEventCallback)callback;