3.1 Confirm your phone's operating system version is compatible (Android 9.0+/iOS 13.0+), and update the Haylou Sound app to the latest version; 3.2 Close and reopen the app, or restart your phone's Bluetooth; 3.3 Clear the app cache (Android: Settings → Apps → Haylou Sound app → Storage → Clear cache; Apple: Uninstall and reinstall); 3.4 Disconnect the headphones from your phone's Bluetooth connection, re-pair them, and then connect to the app again.