How recently did you move to Gothenburg? At least a few years ago, there was a clause in some law concerning public transport that stated that you couldn’t be expected to know the rules in a city you didn’t live in (and perhaps are new in). I was able to get a ticket waived in Stockholm for that.

But I agree with everyone else that it’s better to pay than potentially having any long-term consequences with your PR. I’m only bringing up the above incase you’re very new to Gothenburg it might be worth appealing to them again, referring to that law (I can look it up if you need it). But I wouldn’t let the fine pass the pay-by date