The CCS protocol is far more complicated than the J.1772 PWM pilot signal that Openevse supports.
The problem you are having seems to be rather unique to Electrify America, in that they seem to be charging you based on what their DC charger thinks that the vehicle is capable of drawing, rather than what the vehicle actually draws during the charging session. I'm not aware of any other charging network that has a tariff that works like you describe for Electrify America.
I am aware of charging networks that have different tariffs for different DC chargers at the same site, depending on the maximum power available from there.
350kW capable charger = $$$ / kWh
125kW capable charger = $$ / kWh
50kW capable charger = $ / kWh
which encourages drivers of less-capable vehicles to choose a lower-power charger when possible.
It seems that Electrify America have recently simplified their tariffs anyway wherever they can legally charge per kWh, they will. Seems to vary on a per-US state basis.
I have a Hyundai Ioniq ZEV and for some crazy reason all Ioniq ZEVs communicate with the EA CSS stations as a 125kW Power level while in fact it only could pull a max of 75kW anyway.
EA blames Hyundai and Hyundai is mum about it.
EA's 50/75kW prices are cool however with this small glitch the communications the 125kW upgrade is not cool.
I would like to
1. Build a CSS vehicle simulator and check if EA is honest and if not probably start on a project towards a class action suite.
2. If EA is honest, design a translator that actually sends EA 75kW signal instead of the 125kW that EA says it gets
Nothing in the J1772 docs for Level1/2 mention the vehicle talking about what Amperage it will pull but maybe the CSS protocol does.
So any info in this direction would be appreciated.