''Why it looks like I can't make this Purchase?''

by SafeX

So, you’ve successfully installed the TWM Wallet, been mining SFX for several years and now have a nice stash of coins, and you're excited about the chance to buy a product listed on Safex Marketplace.

You click the Buy button and get these errors, one after the other:

Don't worry: these errors will affect very few people, and if you are one of them - we have provided a solution. It might occur if you have been mining for a long time and never changed the default pool payout. Let's dive into the details:

What has happened here?

The key to understanding this error sequence is contained in the second error screen - Advanced tx too big. Create bigger input.

Each time you receive coins in your wallet address, they arrive as outputs, according to each numerical unit. This is due to the use of the CryptoNote system of tracking the coins on the blockchain.

Safex uses the CryptoNote system of outputs for recording coin movements into and out of the wallet. If you receive 124658 SFX in a transaction, CryptoNote would register the incoming coins as the following 6 outputs against your Safex Address:

  • 100000
  • 20000
  • 4000
  • 600
  • 50
  • 8

Every incoming transaction is similarly registered, and all the outputs are then available as inputs when you subsequently make an outgoing transaction. (Coin outputs become inputs when put IN to a transaction you send from the wallet.)

This input/output system of CryptoNote has been explained in greater detail here.

Every input in a transaction requires an amount of data and needs to be identified (including its Key Image, to avoid Double Spend issues.). There is a data/size limit to how many inputs can be in a single transaction.

If just doing a simple Send transaction from the wallet, you can specify any number of coins in your balance that you wish to send, and the wallet will send those coins to the Safex address you nominate, even if the wallet has to create multiple transactions to accommodate all the inputs needed to accomplish the Send request.

However, Advanced Transactions, such as a Purchase, can only be completed with a single transaction. This means the SFX needed to cover the purchase price must fit into that one single transaction. Therefore, the number of inputs that need to be identified (data) must likewise fit within the single transaction-size parameter, including the data needed to identify the product being purchased.

You will receive this error sequence in the TWM Wallet when there are too many small outputs in your wallet, meaning the number of inputs required exceeds maximum transaction size. If you have fewer, larger outputs in your wallet, it takes less inputs, and correspondingly less data, to form the transaction.

How did this issue arise?

This is normally only an issue where you left mining payouts small, and accrued multitudes of them.

If you have been mining since the launch of the blockchain in 2018, then there’s a good chance you simply set your PC to mining and didn't bother changing the default pool payout. Back in those early days, the popular SafexNews.pool had a default payout of 2 SFX, which meant every time your mining balance went above 2, you were sent a payout to your wallet address.

More recently, Safex.org pool has a default payout of 15 SFX, but again, that is still a very small number (becomes two outputs: 10 + 5).

This means that miners who left their pool payouts at the default setting have been accumulating huge numbers of very small outputs in their wallets.

How To Resolve?

The first thing to try is simply lower the mixin value on the Purchase attempt. But, if you reach mixin 1 and get the same error, then, as the error says, you need to Create bigger input.

This can be accomplished by sending the bulk of your SFX to your self same address.

Ensuring you leave a little SFX aside to cover the transaction fees, send the bulk (all except about 20 will do) of your total SFX to yourself (same wallet address) at mixin 1.

The wallet will automatically create multiple transactions, if needed, from the one send request, in order to accomplish the request.

Even at mixin 1 it will likely cost you maybe a few SFX in tx fees to upsize your outputs.

All the little outputs in your wallet will get spent, and when your SFX returns, they’ll be in bigger-sized outputs.

Once the SFX returns to your wallet and becomes available (after 10 blocks), you will be able to make your purchase.

Final Note

You don't want to repeat the problem in the future. If you haven’t increased your mining pool payout, get in there and increase it. Seeing lots of pool payments arriving every day is exciting, but having bigger payments arriving less often is much better for your future ease-of-spending of those coins.

In the author’s opinion, anyone mining with a Ryzen 9 3900X or similar rig should be setting the payout figure to 1000+, otherwise you will just be inundated with a pile of tiny outputs.

Happy Safex.Market Shopping :)