How to make a bitcoin transaction and pay less than 1 sat/vByte

[Pmalek]

If your transaction is not signed with SIGHASH_ALL, then it matters, because other nodes can change it, and batch many transactions into one, or solve your "sighash puzzle", and broadcast it on-chain.

Do you know of cases where mining nodes have done that? I mean, for regular people like you and me and not with their own transactions or those from people connected to them in some ways. A mining node can include any valid transaction into a block they mine, but why would they do that with mine transaction? There are other transactions already paying higher fees waiting for confirmations, so why waste time to batch below 0.1 sat/vByte transactions into one?

[stwenhao]

Do you know of cases where mining nodes have done that?

Miners can include the final transaction, with high fees, that will be broadcasted by the last user. They don't have to participate in transaction batching, if they don't want to.

Then, it is all about regular, non-mining nodes, and their ability to find transactions, which could be open for modifications, and joining them, and then broadcasting a different version through full-RBF.

A mining node can include any valid transaction into a block they mine, but why would they do that with mine transaction?

Because by batching transactions, you can decrease their on-chain size. Which means, that you have exactly the same fees, but feerate can increase, if the final transaction will take less bytes than before.

why waste time to batch below 0.1 sat/vByte transactions into one?

Because then, users can pay for example 0.09 sat/vByte, 0.08 sat/vByte, or even lower fee rates, and after batching, they will see it as 0.1 sat/vByte transaction, for all participants. In general, I still think that going below 1 sat/vByte is a mistake in the long-term, because people should be focused on batching instead. Then, fees per user can be low, but fee per transaction can be higher, if enough people will join, and if enough things will be stripped (if you have Alice -> Bob -> Charlie, you don't have to put Bob on-chain, as long as coins are flying in the way he wanted).

[Pmalek]

Miners can include the final transaction, with high fees, that will be broadcasted by the last user. They don't have to participate in transaction batching, if they don't want to.

Then, it is all about regular, non-mining nodes, and their ability to find transactions, which could be open for modifications, and joining them, and then broadcasting a different version through full-RBF.

This all sounds like a theory based on the technical capabilities of what the Bitcoin network can do. But as I asked earlier, does this happen in practice? Do you have proof and examples of transactions where individuals engaged in batching and/or modifying transactions with the aim of decreasing their on-chain size? Are there forum threads, communities or blog posts where this approach is explained in more detail and where people have testified that it works?

[LoyceV]

examples of transactions where individuals engaged in batching

Isn't that what coinjoin does?

[Pmalek]

Isn't that what coinjoin does?

If you just mean the batching part, then perhaps. But the entire thing stwenhao talks about isn't a privacy-increasing way of transacting. The primary goal isn't to achieve a higher level of privacy. The idea is for the miners to include transactions that pay more fees in their blocks and save block space, while each individual participant pays less than what they would do on their own.

A coinjoin is also about batching inputs but for the purpose of masking which output belongs to whom. I don't know enough about coinjoins to be able to understand if what stwenhao talks about can be considered a type of coinjoin. Or if his batching and fee & block space preserving technique works in practice. 

[Pmalek]

I downloaded an update to BlueWallet for Android this morning to version 7.2.1 from the Play Store. The wallet now allows to create and broadcast transactions by paying network fees lower than 1 sat/vByte under the condition that you are connected to a node that will relay such transactions. I don't know if the default servers offered by Blue Wallet will relay those transactions or if users will need to manually switch to one that does. The wallet I have there is watch-only, and connected to my airgapped hardware wallet. Blue doesn't have the signing keys, and I am not going to move that stash just for testing. I might transfer some other BTC to a hot wallet on Blue just to test sending a below 1 sat/vByte transaction to see if it works.

Blue Wallet still hasn't updated its release page to add the new version and information about what was changed. A link to download the .apk file for the new Android version is also missing.
https://github.com/BlueWallet/BlueWallet/releases

[TheButterZone]

Nice. OTOH my last attempt to push Blockstream support to add that to Green was 9/10/25, no update since, still erroring when I try to set <1. At least they allow custom Electrum server entry, so the table has been set.

[Charles-Tim]

I downloaded an update to BlueWallet for Android this morning to version 7.2.1 from the Play Store. The wallet now allows to create and broadcast transactions by paying network fees lower than 1 sat/vByte under the condition that you are connected to a node that will relay such transactions. I don't know if the default servers offered by Blue Wallet will relay those transactions or if users will need to manually switch to one that does. The wallet I have there is watch-only, and connected to my airgapped hardware wallet. Blue doesn't have the signing keys, and I am not going to move that stash just for testing. I might transfer some other BTC to a hot wallet on Blue just to test sending a below 1 sat/vByte transaction to see if it works.

Blue Wallet still hasn't updated its release page to add the new version and information about what was changed. A link to download the .apk file for the new Android version is also missing.
https://github.com/BlueWallet/BlueWallet/releases

I tried to send the transaction using 0.4 sat/vbyte with the server Bluewallet connected me to, but it returned a min relay fee error.




I tried to connect to electrum.labrie.ca server but it did not work. Maybe it will later work but it did not work:



I connected to LoyceV Electrum server, electrum.loyce.club and it was connected.



I tried to make the transaction again but it returned min relay fee error.


I closed the Bluewallet app, reopened it and tried it again and it worked with LoyceV server.

[LoyceV]

I connected to LoyceV Electrum server, electrum.loyce.club and it was connected.

In Electrum itself, I only got it to work when I add the port number:

Code:

electrum.loyce.club:50002

Which Electrum itself adds ":s" to:

Code:

electrum.loyce.club:50002:s

it worked with LoyceV server

Good to know my server also works with BlueWallet

[TheButterZone]

Hm, I wonder how BlueWallet's flipping the min relay fee error on and off then. If you need a restart to enable <1 on a <1 server, what if you switch from LoyceV's to a ≥1 server but don't restart before pushing another <1 TX?

[Charles-Tim]

Good to know my server also works with BlueWallet

There are many wallets that are using Electrum server. Bluewallet is one of them.





The transaction is having 2 confirmations already.

Hm, I wonder how BlueWallet's flipping the min relay fee error on and off then. If you need a restart to enable <1 on a <1 server, what if you switch from LoyceV's to a ≥1 server but don't restart before pushing another <1 TX?

LoyceV server is working. I only posted the error to let people know that they have to close the app and reopen it for it to synchronize with LoyceV server.

[TheButterZone]

Hm, I wonder how BlueWallet's flipping the min relay fee error on and off then. If you need a restart to enable <1 on a <1 server, what if you switch from LoyceV's to a ≥1 server but don't restart before pushing another <1 TX?

LoyceV server is working. I only posted the error to let people know that they have to close the app and reopen it for it to synchronize with LoyceV server.

Yes but you should never have to restart any app to sync, that should happen automatically after establishing connection. That's like saying you have to restart Dropbox after you connect to a new WiFi hotspot.

[Pmalek]

I tried to send the transaction using 0.4 sat/vbyte with the server Bluewallet connected me to, but it returned a min relay fee error.

Thanks. At least now we know that the default one won't relay sub 1 sat/vByte transactions. I wonder if any of the default ones in the list Blue Wallet provides will. Btw, do you remember if the one you were initially connected to and that didn't want to relay the transaction was the one by Foundation Devices?

I tried to connect to electrum.labrie.ca server but it did not work. Maybe it will later work but it did not work.

Perhaps the server was offline or you didn't add the (correct) port. I just tried it now after seeing your post and it connected. But a restart of the app was required.
Thanks for confirming that sub 1 sat/vByte transactions can now be sent using Blue Wallet as well. I will add this info to the OP.

In Electrum itself, I only got it to work when I add the port number:

Code:

electrum.loyce.club:50002

I didn't try it without the port number. I left the port at 50002 and just changed the server name.

Hm, I wonder how BlueWallet's flipping the min relay fee error on and off then. If you need a restart to enable <1 on a <1 server, what if you switch from LoyceV's to a ≥1 server but don't restart before pushing another <1 TX?

Good question! I guess the app would broadcast the transaction while still being connected to the <1 server. Since you didn't restart it, the change was never finalized. Still, who knows. Trying to broadcast could also display an error. 

[Charles-Tim]

Btw, do you remember if the one you were initially connected to and that didn't want to relay the transaction was the one by Foundation Devices?

The server was not mainnet.foundationdevices.com. There was 'b' in the server name and the name was not as long.

Perhaps the server was offline or you didn't add the (correct) port. I just tried it now after seeing your post and it connected. But a restart of the app was required.

I tried both 50001 and 50002.

[Pmalek]

I have updated the OP and added a step-by-step guide on how to create sub 1 sat/vByte transactions using Blue Wallet.


How to send a bitcoin transaction and pay less than 1 sat/vByte with Blue Wallet?

The 7.2.1 version of Blue Wallet supports creating and broadcasting transactions that pay less than 1 sat/vByte in fees. You must be connected to a configured server that will allow you to send such transactions. Here is how to set it up.

1. Log in to your Blue Wallet.
2. Click the three dots in the top right corner.
3. Click on "Network" and then on "Electrum Server."
4. You will need to enter a server and port number under "Preferred Server" of one that will relay sub 1 sat/vByte transactions. You can enter electrum.loyce.club or electrum.labrie.ca as those two have been confirmed to work. Enter 50002 as the port number.
5. Click on "Save."
6. If done correctly, Blue Wallet will show a notification that the server was changed.
7. Restart the app for the changes to be saved.
8. Check the server settings after restart to see if you are connected and the server is online.
9. Create and broadcast your transaction as you normally would.

[jukheer]

Latest Sparrow Wallet 2.3.0 supports sub-1sat/vByte:

Support creating transactions with the minimum relay fee rate set by the connected server or configured by the user (with minRelayFeeRate)

[Pmalek]

Latest Sparrow Wallet 2.3.0 supports sub-1sat/vByte:

Support creating transactions with the minimum relay fee rate set by the connected server or configured by the user (with minRelayFeeRate)

Sparrow Wallet already added support for sub 1 sat/vByte transactions back in July in a non-official release, 2.2.4. Users could download it from here:
https://github.com/craigraw/beta/releases/tag/2.2.4-support-minrelaytxfee

The 2.2.4 version had pretty much the same message:

Support creating transactions with the minimum relay fee rate configured by the user or set by the connected server

This is now the first official release that's added the feature.

Thanks for the info!

[satscraper]

This is now the first official release that's added the feature.

If 2.3.0 client connects to node that hasn't adjusted the relay fee rate, then the minimum limit for the relevant fee slider in Sparrow remains 1 sat/vB, and the 'Create Transaction' button is not activated.

Thus, to send a transaction with a fee rate less than 1 sat/vB, your client needs to connect to node that allows the relay of such transactions.

In my case, I have adjusted my own Bitcoin Core v.29.0 node by adding the following entry into the bitcoin.conf file:

Code:

minrelaytxfee=0.00000010

and got the expected result for Sparrow v.2.3.0

[Pmalek]

If 2.3.0 client connects to node that hasn't adjusted the relay fee rate, then the minimum limit for the relevant fee slider in Sparrow remains 1 sat/vB, and the 'Create Transaction' button is not activated.

That's right. That condition has not changed and is the same as it was in the unofficial 2.2.4 release of Sparrow Wallet. You must configure your node to accept below sub 1 sat/vByte transactions to be able to create them in the software client or connect to one that you know has already made those configurations.