There are different settings in the app, that's connected to your charger. Sometimes, these settings have an impact on your charging access, and have to be checked if charging somehow does not start. Follow the guide below, to check your charger settings:
If all of the above is checked, ask the customer to restart the app. The app should work after a soft restart. If this doesn't help, the problem lies elsewhere, and the chargebox might need a troubleshooting.