Bitcoin fees are set by an auction for block space. A payout priced for a quiet moment can sit in the mempool for hours when demand spikes. Replace-by-fee (RBF) is the standard way out.
What replace-by-fee does
A Bitcoin transaction spends specific coins (inputs). RBF builds a new version of the same transaction, spending the same inputs to the same recipient for the same amount, with a higher fee taken from the change. Miners prefer the better-paying version, and because both spend the same coins, only one can ever confirm. The recipient can't be paid twice.
How Valtu uses it
- Every Bitcoin payout is built so it can be replaced: it records its coins and which output is change.
- If a payout is still unconfirmed 30 minutes after broadcast (roughly three blocks), Valtu re-prices it at a higher fee rate and broadcasts the replacement.
- The replacement keeps the same coins and pays the same recipient the same amount; only the change, and so the fee, changes.
- Your transfer keeps one id. Its record lists the replaced transaction hashes, and the webhook reports the hash that confirmed.
Coins in flight are never spent twice
While a payout is unconfirmed, its coins are reserved: the next payout waits for confirmed change rather than spending the same coins. This is what keeps rapid payouts from conflicting with each other.
When RBF can't help
If a transaction has no change output, there is nothing to raise the fee from, so it can't be bumped this way. Sizing payout wallets so payouts leave change avoids that.
More on Bitcoin in Valtu: Bitcoin network · BTC payments.