If you swipe Money Button a lot in a short period of time, you may get an error and have to wait about ten minutes before you can swipe again. This “speed limit” error is not related to Money Button itself, but is caused by a scaling limitation in the Bitcoin SV node software. It is not possible to send more than twenty-five unconfirmed transactions in a chain per block with the current version of the Bitcoin SV node software. Fortunately, you can work around this using our new UTXO management tool to split your UTXOs.

If you expect to swipe Money Button a lot soon, such as uploading a large multipart file or playing a video game, you can prevent this error by splitting your balance into many UTXOs. Our new UTXO management tool allows you to easily do this by simply swiping Money Button once, which sends your own balance back to yourself in ten different outputs. After splitting your UTXOs into ten outputs, you can then swipe Money Button ten times as often per block.

If you have already encountered this error and cannot send payments right now, all you need to do is wait until the next block (about ten minutes on average) and you will be able to swipe Money Button again. You can monitor blocks on any block explorer, such as whatsonchain.com. After the next block, we recommend you use the UTXO management tool to split your UTXOs before your next swipe. Your balance will be unchanged after splitting your UTXOs except for a very small fee to miners.

Why does this error exist?

An earlier generation of Bitcoin node developers created complicated logic around chained transactions involving a concept of “Child Pays for Parent”, or CPFP. The idea of CPFP is that transactions with low fees can be “paid” by a child transaction that contains high fees. Unfortunately, this complicated logic has poor scaling properties and creates a DOS attack vector for large unconfirmed transaction chains. Unwinding this logic and finding a better way to allow CPFP without introducing a DOS attack vector is nontrivial. However, fixing this issue is a high priority for the Bitcoin SV node developers and they are exploring all options and working hard to find the best fix as soon as possible. When this issue is fixed, it will no longer be necessary to manually split your UTXOs.

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1 Comment

  • zhell
    Posted July 9, 2019 at 10:10 am 0Likes

    Moneybutton could automatically detect when the next swipe is going to create the 25th unconfirmed transaction, and if no other UTXO is available, use that 25th to send your own balance back to yourself in ten different outputs, then use one of these other outputs to pay for the original swipe that was asked.

    This would allow to remove the burden of dealing with this problem from the user experience by automating it on the backend side.

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