The charge box might have lost connection to the back-end, mostly due to poor cellular- or WiFi connection. 


The customer can restart the charger by switching off the relay on their switchboard and switching it on again. This prompts the charger to restart, reconnect to the back-end and send a new "Boot notification".  


If problem persists, you will need to connect the charge box to the home WiFi network of the customer - or ask the customer to improve the signal strength, if the charge box is already connected to WiFi.