It will call one of these:
/* Called on the delegate of the receiver. Will be called on startup if the incoming message caused the receiver to launch. */
- (void)session:(WCSession *)session didReceiveMessage:(NSDictionary<NSString *, id> *)message;
/* Called on the delegate of the receiver when the sender sends a message that expects a reply. Will be called on startup if the incoming message caused the receiver to launch. */
- (void)session:(WCSession *)session didReceiveMessage:(NSDictionary<NSString *, id> *)message replyHandler:(void(^)(NSDictionary<NSString *, id> *replyMessage))replyHandler;
/* Called on the delegate of the receiver. Will be called on startup if the incoming message data caused the receiver to launch. */
- (void)session:(WCSession *)session didReceiveMessageData:(NSData *)messageData;
/* Called on the delegate of the receiver when the sender sends message data that expects a reply. Will be called on startup if the incoming message data caused the receiver to launch. */
- (void)session:(WCSession *)session didReceiveMessageData:(NSData *)messageData replyHandler:(void(^)(NSData *replyMessageData))replyHandler;