RATP cannot touch you, search your belongings, or jail you. RATP is not the police. They cannot take your passport and an RATP fine will not bar you from leaving the country. The police are not going to stop you at the airport. Border Control isn’t going to refuse to let you through. They will threaten you, they will try to intimidate you. I’ve seen stories of women being berated, of being scared by the behavior they exhibit. You can walk away from RATP. Their power stops once you leave the metro.

And most importantly, if you feel that you must pay the fine (why), do not give them cash.