If the Xiaomi Robot Vacuum S40 can't be charged, please refer to the following steps:
1. The charging dock is not powered on. Please confirm whether the power cord of the charging dock is inserted at both ends.
2. Please clean the charging dock spring and the charging contact of the robot vacuum;
3. Check for any visible damage or loose connections on the robot vacuum or the charging dock. Examine the charging cable for any signs of damage or fraying;
4. Ensure that the robot vacuum is properly aligned on the dock.
If the above steps cannot resolve the issue, please contact the local after-sales service center for further assistance.