> For the complete documentation index, see [llms.txt](https://sub2.gitbook.io/sub2/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://sub2.gitbook.io/sub2/concepts/fee-auction.md).

# Fee auction

When a subscription is due for payment it enters auction mode. The duration of auction mode, e.g. 30 minutes, is specified by `auctionDuration` in the Subscription struct and is set upon creation. During auction mode, anyone can call `processPayment` on the subscription and be rewarded with the processing fee. Over the duration of the auction period, the amount that the processor is rewarded increases linearly from 0 to `maxProcessingFee`. Thus if the processing fee is sufficient to make it profitable to call `processPayment` for any processor, then the subscription should be processed assuming that no actors leave money on the table. In the event that the payment for a subscription is not processed within the auction time, the subscription will expire.

The fee auction ensures a fair and open process to who gets to process each payment. It comes with strong guarantees against censorship as it only requires one honest processor that is willing to take the processing fee.