You can try entering "0000". If the error still persists, it can be due to abnormal Bluetooth data on the device. Try deleting previous connection records on the device. Then, place the earbuds in the charging case, press and hold the button for 10 seconds until the indicator on the charging case flashes 3 times, then release it and use the device to search for earbuds to pair.
Note:
To delete the Bluetooth records on the phone, go to the [Settings] APP on the phone >> select [Bluetooth] >> [Redmi Buds 6 Lite] >> tap the [Unpair] icon at the bottom.