If you are subject to a fine on board, you must pay it immediately. If you fail to do so, depending on the country or railway undertaking, the fine may be increased.
If you wish to contest the fine:
- be aware of the usually fairly short deadlines. This is normally mentioned on the receipt that was given to you or, if not, on the website of the railway undertaking which issued the ticket.
- Contact the railway undertaking responsible for the ticket inspector (which is not always the one who sold the tickets or owns the train, especially on cross-border journeys).
- Use the online form on the railway undertaking’s website after checking that it is suitable for this type of request.