Has anyone worked on a app to manage tesla wall connectors?

Hey people,
I got a request from a potential client to build him a mobile app that allows users to use tesla wall connectors in located in his gas stations, but he wants to charge them for the service and he wants to prevent users from charging in case they don't provide a payment method and don't have enough funds to pay for the price.
I have 2 issues:
1. How to communicate with the wall connectors, I cannot find any API in the web anyone aware if there is documentation for that somewhere?
2. You wouldn't really know how much the user will be charged in the end. I don't know if such connectors provide you information like how much % is the current battery of the car and how much you want to charge and also how much wh does it take to charge a 1% so that you can calculate the max price and also current price in case user wants to stop charging earlier.
Any resources are appreciated.