Providing a physical charging tag can speed up the 'work' greatly before one can start charging. i found this especially needed in regions/places with a bad network coverage.
I have so many cards so even if you guys added the option to add an existing card to the app like genie point do it could be helpful if the internet is a bit dodgy.
Using NFC of the phone is also OK. Some chargers have no ID on it and cannot be identified in app.