Imagine you send a Bitcoin transaction to your friend. You eagerly wait for it to be confirmed, but it gets stuck in the mempool.

Why? Because the fee you set was too low, and miners aren't interested in including it in a block.

The Problem

Your transaction is sitting in the mempool, unconfirmed for 48 hours. Frustrated, you wonder why it's taking so long. The answer is simple: your transaction fee is too low, and no miner is picking it up.

The Solution: RBF

To fix this, you can use Replace-By-Fee (RBF). RBF allows you to replace your stuck transaction with a new one that offers a higher fee, making it more attractive to miners.

How Does RBF Work?

To increase the fee, you create a conflicting version of the transaction. This new transaction spends at least one of the same UTXOs as the original transaction you want to replace.

By doing this, you signal to the network that your transaction can be replaced by one with a higher fee.

Types of RBF

1. Opt-in RBF: Here, the transaction must specify and signal to miners that it can be replaced by a higher fee transaction. This is done by setting the nSequence to a value below 0xffffffff.

2. Full RBF: Any unconfirmed transaction can be replaced without signaling. This method offers more flexibility but may face network policy restrictions.