It's tempting to throw the fine in a drawer. But in Belgium, unpaid fines tend to grow and escalate rather than disappear. Here's the realistic picture.
Parking retributions
If you don't pay or contest, the agency sends a reminder, then a formal notice. After roughly 30 days it can issue a "constraint" served by a bailiff, adding significant costs. The original €25–€35 can balloon.
GAS / SAC fines
Ignore the sanctioning official and the fine becomes final and enforceable, again with possible bailiff collection.
Penal (police) fines
An unpaid police settlement goes to the public prosecutor and can end up before the Police Court, where the amount rises and a conviction is possible.
The smarter move
If the fine is wrong, contest it on time — it's free and often works. If it's valid, paying early (within the deadline) usually keeps it at the lowest amount and stops the costs. Either way, doing nothing is the most expensive option.
Not sure which case you're in? Quitte reads your fine and gives an honest pay-or-contest verdict in a couple of minutes.