You sent some BTC from your wallet, but it didn’t go through. You waited a while, but the person you sent it to didn’t receive anything. How come? And how can you be sure that all the funds you send will reach their intended destination?
It’s important to remember how transactions are processed. First of all, the transaction is sent to all miner nodes and placed in a queue for processing, known as a mempool. Miners consolidate several thousands of transactions into a draft block for the blockchain and try to ‘mine’ it. When one of them is successful, the transaction is entered into the block and the miner receives a commission for processing it.
The commission is the key thing here. If the sender wanted to save money and set a small reward, the transaction would have a lower processing priority. The size of the commission isn’t fixed, however, and depends on the network load.
If you need to send cryptocurrency as quickly as possible, you should therefore choose the current ‘ballpark’ reward amount or higher. You can find out the current levels using specialist services. In our mobile app, the fee is calculated automatically and you can set the priority level at ‘Low’, ‘Standard’ or ‘Priority’.
So what happens when you’ve set a low commission, the network is experiencing high loads and your crypto assets get ‘stuck’? If you decide to play the waiting game, there are two options: 1) the transaction will be processed, but there is no way of knowing how long it will take; 2) the transaction will be ‘evicted’ from the mempool (this usually takes around 48 hours) and the cryptocurrency can be used again.
You can solve this by using the Replace-By-Fee (RBF) feature. This involves creating another transaction with a higher commission. Since all the parameters (inputs and outputs) remain unchanged, it will be perceived by the nodes as identical to the old transaction, but the larger commission means it will receive a higher priority in the mempool. It should be noted, however, that not all wallets support RBF.
Another method is Child-Pays-For-Parent (CPFP). This involves creating a child transaction with a higher commission. The trick lies in the fact that the new transaction must be sent to the ‘change address’ of the one that’s stuck (in essence, we are sending the cryptocurrency to ourselves, but ‘tying’ the transaction to the previous one). The reward amount should be set at a level that covers both transactions and is high enough to be attractive to miners. Since the child transaction cannot be confirmed without the parent transaction being confirmed, both will be processed.
You can also use transaction accelerators. All you need to do is feed them the TXID of the transaction that’s become stuck, and everything else rests with the accelerator.
Some simply relay the transaction across the network nodes, reminding the miners of its existence and returning it to the mempool. Others are mining pools (or use partner pools) that, for a fee, insert the stuck transaction into the next block to be mined.
ViaBTC is one of the oldest and most popular mining pools. Its Transaction Accelerator service has both free and paid versions. The free version is limited to 100 transactions per hour for everybody. When the network load is particularly high, it can be difficult to make it into this group of 100.
Since the counter is reset every hour, it might make sense to start trying to add the transaction’s TXID during the last few seconds of the hour. Even this approach isn’t guaranteed to work, however, and it might require a few attempts. Another drawback of the free version is that it uses ViaBTC’s own computing power, while the paid acceleration service uses additional partner pools.
The cost of the paid accelerator depends on the network load, cryptocurrency prices and, according to the service description, ‘other factors’. At the time of writing, the commission was around USD 40 in cryptocurrency equivalent.
Another accelerator, offering two types of acceleration. With no reward staked, it simply relays the transaction to the network. For the equivalent of USD 25, it can include it in the next block mined by its partner pools. BTC Nitro guarantees confirmation of the transaction within 24 hours, failing which it promises to return the commission to the user.
A free service that relays the transaction through 10 public nodes. The creators of the service recommend using it for stuck transactions every six hours.
Important! before using paid accelerators (especially those you aren’t familiar with), do a basic background check. Look for the domain registration date and reviews on forums. There have already been cases of fraudsters hiding behind accelerators. One example is Confirmtx, a service that successfully launched in 2017, was reviewed several times and featured in a number of articles, and was then caught committing fraud. The owners, of course, were simply collecting the money without accelerating anything.