I have implemented a very simple iOS + WatchOS app project, where I test how one can communicate with the other. I will paste the code below, but the idea is really simple. Each app has one single screen with a button and a label. Tapping the button will send a message to the counterpart indicating the timestamp when the message was generated. If I run the app on the simulators, everything works fine: messages are sent and received correctly on both the iPhone and the Watch. (You can find a reference gif on imgur.com/ + o1ZQTLp). The problem occurs when I try to run the same apps on my physical devices. Session is activated successfully but messages aren't sent. If I debug the code, I even see the WCSession.isReachable value set to true. When debugging the WatchKit app, I see errorHandler is called on the func sendMessage(), and the error states: WatchConnectivity session on paired device is not reachable. However, the errorHandler isn't called from the iPhone app. Details of my devices: iOS version: 14.0.1 WatchOS version: 7.0.1 I tested this same code before installing the 7.0.1 WatchOS and it worked without any problems, so I wonder if the update introduced some error on the WatchConnectivity framework. Code on the iPhone app: import UIKit import WatchConnectivity class ViewController: UIViewController { 		@IBOutlet weak var messageLabel: UILabel! 		fileprivate var wcSession: WCSession! 		override func viewDidLoad() { 				super.viewDidLoad() 				wcSession = WCSession.default 				wcSession.delegate = self 				wcSession.activate() 		} 		@IBAction func sendMessageAction(_ sender: Any) { 				let message = [ 						"content": "Message sent from iPhone on \(Date())." 				] 				wcSession.sendMessage(message, replyHandler: nil, errorHandler: { error in 						print("Error when sending message: \(error.localizedDescription)") 				}) 		} } extension ViewController: WCSessionDelegate { 		func session(_ session: WCSession, activationDidCompleteWith activationState: WCSessionActivationState, error: Error?) { 				switch activationState { 				case .activated: 						print("WCSession activated successfully") 				case .inactive: 						print("Unable to activate the WCSession. Error: \(error?.localizedDescription ?? "--")") 				case .notActivated: 						print("Unexpected .notActivated state received after trying to activate the WCSession") 				@unknown default: 						print("Unexpected state received after trying to activate the WCSession") 				} 		} 		func session(_ session: WCSession, didReceiveMessage message: [String : Any]) { 				guard let content = message["content"] as? String else { return } 				DispatchQueue.main.async { 						self.messageLabel.text = content 				} 		} 		func sessionDidBecomeInactive(_ session: WCSession) { 		} 		func sessionDidDeactivate(_ session: WCSession) { 		} } Code on the Watch Kit app: import WatchKit import Foundation import WatchConnectivity class InterfaceController: WKInterfaceController { 		@IBOutlet weak var messageLabel: WKInterfaceLabel! 		fileprivate var wcSession: WCSession! 		override func awake(withContext context: Any?) { 				wcSession = WCSession.default 				wcSession.delegate = self 				wcSession.activate() 		} 		@IBAction func sendMessageAction() { 				let message = [ 						"content": "Message sent from Watch on \(Date())." 				] 				wcSession.sendMessage(message, replyHandler: nil, errorHandler: { error in 						print("Error when sending message: \(error.localizedDescription)") 				}) 		} } extension InterfaceController: WCSessionDelegate { 		func session(_ session: WCSession, activationDidCompleteWith activationState: WCSessionActivationState, error: Error?) { 				switch activationState { 				case .activated: 						print("WCSession activated successfully") 				case .inactive: 						print("Unable to activate the WCSession. Error: \(error?.localizedDescription ?? "--")") 				case .notActivated: 						print("Unexpected .notActivated state received after trying to activate the WCSession") 				@unknown default: 						print("Unexpected state received after trying to activate the WCSession") 				} 		} 		func session(_ session: WCSession, didReceiveMessage message: [String: Any]) { 				guard let content = message["content"] as? String else { return } 				messageLabel.setText(content) 		} }