When I withdrew my Bitcoin from an exchange (Remitano) to my hardware wallet earlier today, I waited for more than 12 hours but the transaction didn’t have any confirmation. Then when I checked it again, I saw the warning on Blockchain.info.
Warning! this transaction is a double spend. You should be extremely careful when trusting any transactions to/from this sender.
The double spend issue might happen accidentally or intentionally when the sender set the fee too low for a transaction and the same inputs are used on another transaction. In my case, the transaction fee is quite high at 230.973 sat/B, so the double spend is caused by a chain of unconfirmed transactions. This is a common issue and you can see a lot of double spends in this list. As of writing this post, there’ve been 165,172 double spends.
I contacted the exchange to find out the best solution and they told me to keep waiting. If the transaction doesn’t go through after a few days, my Bitcoin will be returned to my web wallet there.
I checked my transaction 2 days later and it was no longer there. I saw the message:
Transaction rejected by our node. Reason: Transaction was previously accepted but has been pruned from our database.
That means this transaction is invalid and therefore, it is not accepted into the mempool. Fortunately, the exchange agreed to send me the bitcoin in another transaction and it got confirmed within 5 minutes. So, the lesson here is to wait until your transaction receives at least 1 confirmation. If you are dealing with a seller on a forum or localbitcoins, your Bitcoin might disappear forever.