Please follow the below steps:
1. It may be that the current network is unstable and the upgrade package you're downloading is damaged. Try using a different network.
2. The battery level of phone (1) is too low. When the power is lower than 30%, the system does not allow OTA to upgrade.
3. The OTA upgrade process may have been interrupted. Try re-upgrading.
If the issue persists, contact the Nothing Support Team for further assistance.