Hello Llouthooboiss27
If you are resident of Switzerland or of any other European country, even short-term only, you are not entitled to use Eurail.
It is stated unmistakenly in the first sentence on the Eurail website:
A Eurail Pass can only be used by non-European citizens or non-European residents
https://www.eurail.com/en/help/interested-in-eurailing/do-i-need-a-eurail-or-an-interrail-pass
Unfortunately, further in the text, Eurail is confusing Europe with EU, while they actually mean Schengen countries; however, the first sentence is not misleading. You should forward your feedback to Eurail.
The fine is justified from my perspective as Eurail cannot be used by people holding a resident permit issued by an European country. As a consequence, you did not have a valid ticket. If you do not agree, please contact the number stated on the invoice. Here, on this platform, we are unable to treat your issue.
For future trips in Switzerland, check for the Half Fare Card, Saver Day Passes (online, advanved booking) or the GA travel card for a month. Best to see a counter agent to help you find the best ticket.
Kind regards,
Roland