To resolve the issue of your JYouPro ring not connecting to the app despite being fully charged, follow these detailed steps:

1. Restart Your Phone: Begin by restarting your smartphone. This can often resolve temporary connectivity issues.

2. Update the JYouPro App: Check if there is an update available for the JYouPro app in your app store (Google Play Store for Android or App Store for iOS). Installing any available updates can fix bugs that might prevent connection.

3. Check Bluetooth Settings: Go to your phone's Bluetooth settings. Ensure that Bluetooth is turned on and that your JYouPro ring is listed among the paired devices. If it is not listed, you will need to pair it again.

4. Forget and Re-pair the Device: If the ring is listed in your Bluetooth settings, long-press the device name and select "Forget" or "Remove". Then, try to pair the ring again:
- Open the JYouPro app and ensure that it is on the pairing screen.
- Put your JYouPro ring in pairing mode (refer to the user manual if you’re unsure how).
- Select the ring from the list of available devices in the app.

5. Enable Location Services: Make sure location services are turned on for the JYouPro app. Some Bluetooth devices require location permissions to function properly. Go to your phone’s settings, find the JYouPro app, and ensure location permissions are enabled - learn more.

6. Clear App Cache (Android Users): If you are using an Android device, go to your phone's Settings > Apps > JYouPro > Storage, and clear the cache and data. This will reset the app without deleting your personal data.

7. Uninstall and Reinstall the App: As a last resort, uninstall the JYouPro app and then reinstall it from your app store. This will ensure a fresh installation with default settings - learn more.

8. Check for Firmware Updates: Sometimes, the issue could be related to the firmware of the ring. Check if there is a firmware update available through the app and ensure that your ring is updated to the latest version.

If these steps do not resolve the issue, consider resetting your JYouPro ring to factory settings. Instructions for this should be available in the user manual. If problems persist, you may want to contact customer support for further assistance - learn more.