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What is a dropped transaction, and what should I do about it?

A pending transaction can be dropped for several reasons. Don't worry, no bitcoin is lost.

When bitcoin transactions are broadcast, they exist in a "pending" state until they are added to the blockchain by bitcoin miners. We often refer to pending transactions as being "in the mempool."

Technically, there is no single centralized mempool. Instead, each bitcoin node has it's own version of a mempool tracking pending transactions. Although nodes share information about these transactions, there's imperfect alignment across the network.

Pending transactions can be dropped from a node's mempool. If you received an email from Unchained about a dropped transaction, it's because the transaction has been dropped from Unchained's mempool. It may still be tracked by the mempools of other nodes.

Why would a transaction be dropped from a node's mempool?

There are typically two reasons a transaction could be dropped from a node's mempool:

  1. If a node's mempool is full of pending transactions, the node may begin dropping transactions with the lowest fee rates.
  2. A "replace-by-fee" (RBF) transaction is a technique that replaces an old transaction with a new one, often to increase the fee rate, or to change details about a pending payment. In this case, the old transaction is eventually dropped.

Note: Some bitcoin exchanges, such as Strike, frequently use RBF to facilitate customer withdrawals. For an Unchained vault, this could trigger several different notifications of incoming deposits, followed by several "dropped transaction" notifications.

What should I do about a dropped transaction?

If you're trying to receive bitcoin to an Unchained vault or loan, and you notice dropped transaction notifications, you can enter that vault or loan to see if you've successfully received the bitcoin you were expecting. If so, there was likely an RBF involved, and you may disregard the notifications.

If you have not received the bitcoin you were expecting, it could be the case that the sender used too low of a fee rate for the transaction. You can discuss the matter with the sender, and perhaps request a new transaction with a higher fee rate.

Caution: For more information about how to safely receive bitcoin, see our comprehensive article. Never consider a transaction completed until it's been confirmed on the blockchain.

If you're trying to send bitcoin from an Unchained vault or loan, and notice a dropped transaction notification, it's likely because the fee rate for the transaction was too low. If you enter your vault, it will appear like the withdrawal never occurred.

In cases of both sending and receiving, it's possible to attempt some advanced strategies to find the dropped transaction on another node and increase the fee rate so that the transaction is mined into a block. If you would like guidance doing this for a transaction associated with an Unchained vault, please reach out to our support team.