How is this possible ? A Recent transaction suddenly becomes invalid

[HelpMePleaseIbegofYou]

hello everyone, Good evening

sorry to bother you about this issue i got from a customer. i sold a product to him for $100
i gave him wallet and he sent btc $100 and paste me txid which i saw the payment in my wallet ( Unconfirmed )

surprisingly, this guy logoff the chat and i wonder why he left so hurriedly just after i gave him the passwords to the achieved file.

i had to recheck if the payment has gotten any confirmation but surprisingly this transaction stated its INVALID with a error message at the top of the page
rechecked my wallet and i did not see the transaction again. 

below is the txid of the transaction, you can see the error message there.

https://www.blockchain.com/btc/tx/2f362caac5d3fa3a1cc586f5bdbb36bcfe6446cfc112eb1cb097d9669688204a

my wallet:  34Y9ZwTsT3H9zcnffirc2NM4XMkNmaLws6

Please. how is this possible. i really want to know this to avoid another of this.

chat screenshot
https://i.imgur.com/GLy3rhD.png

[1714986105]

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[1714986105]

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[AB de Royse777]

https://www.blockchain.com/btc/tx/2f362caac5d3fa3a1cc586f5bdbb36bcfe6446cfc112eb1cb097d9669688204a

my wallet:  34Y9ZwTsT3H9zcnffirc2NM4XMkNmaLws6

You should have wait for at least 1 confirmation unless you trust the guy. This is what happened in my guess:

- The guy sent coins to an address A which he owns and the fees were less of course
- He then sent the coins from the address A, and the coins of the address A (input)were not confirmed yet.
- He then gone back to the first transaction and rebroadcast the first transaction with a higher fee. And in rebroadcasting process, the tx you had with address A gone dropped.

[so98nn]

https://www.blockchain.com/btc/tx/2f362caac5d3fa3a1cc586f5bdbb36bcfe6446cfc112eb1cb097d9669688204a

my wallet:  34Y9ZwTsT3H9zcnffirc2NM4XMkNmaLws6

You should have wait for at least 1 confirmation unless you trust the guy. This is what happened in my guess:

- The guy sent coins to an address A which he owns and the fees were less of course
- He then sent the coins from the address A, and the coins of the address A were not confirmed yet.
- He then gone back to the first transaction and rebroadcast the first transaction with a higher fee. And in rebroadcasting process, the tx you had with address A gone dropped.

That’s amazing way to cancel it however I did not know this can be done with the bitcoin chain as well ?
I mean I have done this in case of Ethereum transaction but never with bitcoin.

What is the exact principle behind this technique? Isn’t the transaction once broadcasted is captured with the nodes and it permanently sits there?

[Lucius]

If I'm not mistaken, this is a double-spend transaction that was performed in a very simple way. Customer is first sent the transaction with very low fee (1.004 sat/B), and after he receives file he generated another transaction with the same funds, but this time with a much higher fee (20.191 sat/B) -> https://www.blockchain.com/btc/address/1CKnhZmHzj45xdvvsAf3DbLWfYSX53NVMs

This is a lesson that only cost $100, I hope this is the first and last time the OP will send someone something without getting at least 1 confirmation.

[AB de Royse777]

What is the exact principle behind this technique? Isn’t the transaction once broadcasted is captured with the nodes and it permanently sits there?

It does but it needs at least 1 confirmation. But here again one can also reverse the coin after a confirmation but it will cost you so much power and resources that if this is not huge amount of money then it is not worth it. Once a transaction gets 6 confirmation then you are looking at million dollar expense to reverse the transaction which is does not simply make sense to spend.

For small amount it is advisable to wait for at least one confirmation and for big amount waiting for 6 confirmation is safe.

[HelpMePleaseIbegofYou]

Thanks so much guys. really do not know Double Spend can do this. but really such feature does not make good to me.
replace by fee feature is Ok and helps when you want to accelerate confirmation. this double spend..whats the benefit ? only good for cheating or ?

[AB de Royse777]

Thanks so much guys. really do not know Double Spend can do this. but really such feature does not make good to me.
replace by fee feature is Ok and helps when you want to accelerate confirmation. this double spend..whats the benefit ? only good for cheating or ?

It was a replace by fee and he has done it with the first transaction which was to the address A in my example. But since the other transaction which gone from address A and the input of A which is the output of first transaction was changed hence the tx that was to you was dropped.

The idea is a miner needs to pick up the transaction.

[bL4nkcode]

this double spend..whats the benefit ? only good for cheating or ?

There's no benefit of double-spending unless you want to cheat and scam people. That's why people should always make this a practice to wait at least 1 confirmation before you consider the transaction valid. Exchanges accept a transaction/deposit at least 3-6 confirmations before it reflects on the user's account.

[logfiles]

Thanks so much guys. really do not know Double Spend can do this. but really such feature does not make good to me.
replace by fee feature is Ok and helps when you want to accelerate confirmation. this double spend..whats the benefit ? only good for cheating or ?

It's actually the Replace by fee exploit that is used to carry out such a type of double-spending. Minus their unconfirmed transactions being RBF enabled, the cheat wouldn't have been able to rebroadcast a new transaction with higher fees. Just like anything else, there are always pros and cons. You have just got to be smart to avoid getting scammed 

[o_e_l_e_o]

It was a replace by fee and he has done it with the first transaction which was to the address A in my example. But since the other transaction which gone from address A and the input of A which is the output of first transaction was changed hence the tx that was to you was dropped.

I don't think it was. It looks like a fairly standard double spend.

The sender had 0.10494256 BTC in one output on address 1CKnhZmHzj45xdvvsAf3DbLWfYSX53NVMs. This output already had 100+ confirmations.
He made an initial transaction to OP with TXID 2f362caac5d3fa3a1cc586f5bdbb36bcfe6446cfc112eb1cb097d9669688204a, which spent that output with a fee of 1 sat/vbyte.
He then made a second transaction with TXID 31c444900939113ad1c57277fc2904b20f77e57f76f95eee45ec119e72a6342c, which spen the same output to a different address (presumably his own) with a fee of 20.2 sats/vbyte.

[Findingnemo]

this double spend..whats the benefit ? only good for cheating or ?

Double spending mean cheating but the use of RBF is not really to cheat anyone its to avoid the transaction waiting time, if you made a transaction with lower fee earlier but now you really wants to make it in a hurry then you can simply use the high fee is your wallet supports RBF.When you are in the receiving end never confirm anything until it has one confrimation.

[skarais]

This is the first time I've heard that someone can cancel the first transaction which fee less and be replaced with a second transaction that fee more. This is a valuable lesson I learned today if I wanted to shop online. Before fund enter the wallet, no transaction is secure.
I think it's a trap that anyone looking to sell something online should avoid. I hope there are no other victim with similar cases, and for the OP I hope you can make this a valuable experience in terms of buying and selling online. It's safer to use Escrow if you want to make a larger transaction.

[pawanjain]

This is the first time I've heard that someone can cancel the first transaction which fee less and be replaced with a second transaction that fee more. This is a valuable lesson I learned today if I wanted to shop online. Before fund enter the wallet, no transaction is secure.
I think it's a trap that anyone looking to sell something online should avoid. I hope there are no other victim with similar cases, and for the OP I hope you can make this a valuable experience in terms of buying and selling online. It's safer to use Escrow if you want to make a larger transaction.

It's not cancelling a transaction it's basically rebroadcasting a transaction. It's like redoing your homework when you did it incorrectly the first time.
This is why it is expected for us to wait until 1-2 confirmations to make sure that the transaction is valid and is broadcasted correctly on the blockchain.
And only after 6 confirmations we can conclude that the amount is transferred from his wallet to our wallet.
These are some basic things one should learn before making trading bitcoin.

[Upgrade00]

this double spend..whats the benefit ? only good for cheating or ?

The only legitimate benefit I can think of is to 'unstuck' a transaction.
If I initiate a transaction using a very low fee without setting the RBF option, my transaction is likely going to get stuck, (how long would depend on how clogged up the network is);
• Once a transaction is signed and broadcasted, it is validated by nodes and appears in the mempool, where it would then be picked up by miners and included in blocks for confirmations. A transaction can stay in the mempool for approximately 2 weeks before it is dropped if no miner takes it up.
• To avoid waiting this long the sender can initiate a double spend or use CPFP ~ Child Pays For Parent, to unstuck the transaction. So they send the exact same UTXO to another address and can then perform the initial transaction with a higher fee.

It's not cancelling a transaction it's basically rebroadcasting a transaction. It's like redoing your homework when you did it incorrectly the first time.

Double spend is a bit different from a typical rebroadcast. In double spend you're not rebroadcasting as a new transaction is created with a different output and a much higher fee.

[AB de Royse777]

The sender had 0.10494256 BTC in one output on address 1CKnhZmHzj45xdvvsAf3DbLWfYSX53NVMs. This output already had 100+ confirmations.
He made an initial transaction to OP with TXID 2f362caac5d3fa3a1cc586f5bdbb36bcfe6446cfc112eb1cb097d9669688204a, which spent that output with a fee of 1 sat/vbyte.
He then made a second transaction with TXID 31c444900939113ad1c57277fc2904b20f77e57f76f95eee45ec119e72a6342c, which spen the same output to a different address (presumably his own) with a fee of 20.2 sats/vbyte.

When I responded I did not check the tx but explained the possibility now I see the tx history of that address (output address of the sender).

Tx in question is this: 2f362caac5d3fa3a1cc586f5bdbb36bcfe6446cfc112eb1cb097d9669688204a
and this tx has OPs address 34Y9ZwTsT3H9zcnffirc2NM4XMkNmaLws6

Then the sender somehow removed the OPs address and replaced it with this address 1HrtBS3eM1wG7UKuP39fqnRQVX6FJvc8An
And used higher fees. The tx is 31c444900939113ad1c57277fc2904b20f77e57f76f95eee45ec119e72a6342c

In both cases the change address was the same address as the output which is 1CKnhZmHzj45xdvvsAf3DbLWfYSX53NVMs

First tx (2f362caac5d3fa3a1cc586f5bdbb36bcfe6446cfc112eb1cb097d9669688204a) had less fees and had this address (1CKnhZmHzj45xdvvsAf3DbLWfYSX53NVMs) as changed.
Address 1CKnhZmHzj45xdvvsAf3DbLWfYSX53NVMs has unconfirmed coin, and he went to spend that unconfirmed coin. Once he made the 2nd tx then the first tx was effected because it had its input and output same address. And as a reason the first Tx dropped?

I never experienced that but the dry run takes me to this path for the drop of the first tx. Please correct me where I am wrong.

PS: I might do a test tx to see it myself. This is interesting for me.

[o_e_l_e_o]

Once he made the 2nd tx then the first tx was effected because it had its input and output same address. And as a reason the first Tx dropped?

So the first transaction dropped because the second transaction spent the same input as the first transaction. Once it was spent by the second transaction, it was no longer available to be spent in the first, and so the first became invalid.

Even although the 1CKnh... address still had enough funds on it for the first transaction, they were now part of a different output, and so the first transaction was still invalid. Transactions spend specific outputs. If I have an address with 5 outputs each of 1 BTC, and I make two different transactions using the same output, only 1 will confirm and 1 will become invalid, even though there are 4 other outputs of 1 BTC at that address.

[HelpMePleaseIbegofYou]

The sender had 0.10494256 BTC in one output on address 1CKnhZmHzj45xdvvsAf3DbLWfYSX53NVMs. This output already had 100+ confirmations.
He made an initial transaction to OP with TXID 2f362caac5d3fa3a1cc586f5bdbb36bcfe6446cfc112eb1cb097d9669688204a, which spent that output with a fee of 1 sat/vbyte.
He then made a second transaction with TXID 31c444900939113ad1c57277fc2904b20f77e57f76f95eee45ec119e72a6342c, which spen the same output to a different address (presumably his own) with a fee of 20.2 sats/vbyte.

When I responded I did not check the tx but explained the possibility now I see the tx history of that address (output address of the sender).

Tx in question is this: 2f362caac5d3fa3a1cc586f5bdbb36bcfe6446cfc112eb1cb097d9669688204a
and this tx has OPs address 34Y9ZwTsT3H9zcnffirc2NM4XMkNmaLws6

Then the sender somehow removed the OPs address and replaced it with this address 1HrtBS3eM1wG7UKuP39fqnRQVX6FJvc8An
And used higher fees. The tx is 31c444900939113ad1c57277fc2904b20f77e57f76f95eee45ec119e72a6342c

In both cases the change address was the same address as the output which is 1CKnhZmHzj45xdvvsAf3DbLWfYSX53NVMs

First tx (2f362caac5d3fa3a1cc586f5bdbb36bcfe6446cfc112eb1cb097d9669688204a) had less fees and had this address (1CKnhZmHzj45xdvvsAf3DbLWfYSX53NVMs) as changed.
Address 1CKnhZmHzj45xdvvsAf3DbLWfYSX53NVMs has unconfirmed coin, and he went to spend that unconfirmed coin. Once he made the 2nd tx then the first tx was effected because it had its input and output same address. And as a reason the first Tx dropped?

I never experienced that but the dry run takes me to this path for the drop of the first tx. Please correct me where I am wrong.

PS: I might do a test tx to see it myself. This is interesting for me.

this looks soo like magic LOL..

what i do not understand is this. lets say i have $200 in my wallet on blockchain.info, then i send $100 to someone, even if its unconfirmed or low fee i am sure
the money $100 will be deducted from my account. How is it possible i could spend a money that already deduct from my account and move it to another wallet..

i wish to see a video demonstration of this.  This is very very interesting. very smart trick.

[AB de Royse777]

this looks soo like magic LOL..

what i do not understand is this. lets say i have $200 in my wallet on blockchain.info, then i send $100 to someone, even if its unconfirmed or low fee i am sure
the money $100 will be deducted from my account. How is it possible i could spend a money that already deduct from my account and move it to another wallet..

i wish to see a video demonstration of this.  This is very very interesting. very smart trick.

I am still trying to get this in my head. Very tricky for me to understand although o_e_l_e_o tried to explain in the post above you. I did make a test tx but I messed up with something and now stuck with some error, nothing wrong and it will be confirmed though. I will let this tx to confirm and then try with a fresh one then will share the flow.

So the first transaction dropped because the second transaction spent the same input as the first transaction. Once it was spent by the second transaction, it was no longer available to be spent in the first, and so the first became invalid.

Even although the 1CKnh... address still had enough funds on it for the first transaction, they were now part of a different output, and so the first transaction was still invalid. Transactions spend specific outputs. If I have an address with 5 outputs each of 1 BTC, and I make two different transactions using the same output, only 1 will confirm and 1 will become invalid, even though there are 4 other outputs of 1 BTC at that address.

That error suck me, it is saying not sufficient fund for fees. Not sure if this is connected with the goal I am trying to achieve. But as I said I will try again once the tx confirms.

[o_e_l_e_o]

How is it possible i could spend a money that already deduct from my account and move it to another wallet..

Because until the transaction is confirmed, the money has not left your wallet yet. By broadcasting a transaction, all you've done is essentially send out a message saying "I want to move money from here to there". Until the transaction is confirmed, no money has actually moved.

You can send out two different messages sending the same money to different places. Whichever one is confirmed first is where the money will go, and the other one will be made invalid.

[AB de Royse777]

Because until the transaction is confirmed, the money has not left your wallet yet. By broadcasting a transaction, all you've done is essentially send out a message saying "I want to move money from here to there". Until the transaction is confirmed, no money has actually moved.

You can send out two different messages sending the same money to different places. Whichever one is confirmed first is where the money will go, and the other one will be made invalid.

Correct 100%
In other words, do not complete a deal until the tx has minimum 1 confirmation @HelpMePleaseIbegofYou.
Again sorry for the loss, we all learn from our own experience or someone else's experience.