Warning 10400 means that the main relay of the charger switched at least three times within 15 minutes. To protect the relay, the charger pauses charging for a short time. This can happen when the car repeatedly starts and stops a session, for example during solar charging with a fluctuating surplus.
What to do
Wait. Charging is allowed again and restarts automatically after at most 15 minutes.
If charging does not restart by itself, unplug the charging cable and plug it back in.
For installers and charge point operators: check that the OCPP configuration key WakeupEvPulseInB2 is set to true. With this setting the charger wakes the car up when charging may resume.