If adding a bank card to the Xiaomi Watch S4 41mm fails, please refer to the following information:
1. Try switching to a different network, then tap retry below the error message.
2. Restart your phone's Bluetooth and switch to a different mobile network before trying again.
3. Make sure the watch is properly connected to the phone, then try recharging again in the Mi Fitness App.
4. Check whether the Mi Fitness App is the latest version. Update both the App and the watch firmware to the latest versions and try again.
5. Restart both the watch and the phone before attempting to add the card again.
6. If the card still cannot be added, contact your bank or card issuer to check for restrictions or security blocks.