Likely causes
- Bluetooth or location permission denied for the app
- Device still bonded to another phone
- Device not actually in pairing mode
- Phone Bluetooth stack needs a restart
- Interference or too much distance during pairing
Quick checks
- Turn Bluetooth off and on again
- Check app permissions for Bluetooth and location
- Confirm the device LED pattern for pairing mode
- Try pairing from the phone settings instead of the app
Step-by-step fix
Remove the old bond for the device in phone settings
Force-close the app and reopen it
Put the device back into pairing mode and pair within one metre
Complete the pairing inside the vendor app so the account is linked
If it still fails, test with a second phone to isolate the cause