How do I pay a late-cancellation fee?

Open a game of the organizer you owe it to. The fee appears as a banner at the bottom of the game screen with the amount and the date you cancelled, next to a button to pay and a button to message the organizer.

Paying opens a checkout with the online methods that can actually work for that amount: card, Apple Pay, Google Pay, Telegram, or your Playbox wallet. The wallet is offered only when your balance already covers the fee, and a card is not offered when the fee is below the smallest amount a card payment can process. When a method is unavailable the screen explains why instead of hiding it. Cash is not an option here, because there is nobody at a pitch to confirm it.

If no method can work at all, the pay button disappears and the remaining action is to message the organizer and settle it between you.

Paying is a separate step that comes first: the fee is no longer added to the price of your next game, so settle it and then join.

One payment clears everything you owe that organizer at once, the money arrives in their Playbox balance, and they are notified that you paid. You owe the fee to that organizer, not to Playbox, so if you think it is wrong, use the button on the banner to write to them directly.