You should also contact ChargePoint customer service to notify them of the situation. They have a responsibility to mark the location as private in their app if it is not open for public use. You could also ask them to help offset the fine with a charging credit since you were just trying to use their service.
Good idea, but save this for a last step. Right now, when you are talking to officials, you want the web pages (plugshare, chargepoint, etc.) to look like they did the day of the "violation". Take screen shots of those pages with dates before they might change to "private" or "restricted".
I am actually feeling more optimistic about your chances if Plugshare and chargepoint were advertising public use. I'm not entirely sure about the argument parking versus charging, but I kind of like it combined with the web "advertised" public use aspect. Check to see if the plugshare entry was posted as an "official act" of the municipality.
Definitely, keep all discussions friendly and positive! You may need to start writing letters, however, in my experience, try to solve the problem by phone calls and in person meetings first, if you can. Do keep dated documentation in case you need it later. Keep brief dated notes of all of your meetings and conversations and the substance of the discussion (it gets really difficult to remember those details weeks or months later).
Another (later) step in EV friendly CA, might be to contact the local newspaper, or even a TV station consumer help person. Is there a local EV group?
I think the value of $65 is very relative (esp. relative to hours spent on the project), however, if you are still enjoying the project and do not succeed informally, find out if there is a traffic court, municipal court, or some equivalent to a small claims court. You may even be able (last resort) to sue the municipality
Pro se (without a lawyer).