If there is unconfirmed transaction, coin come back to original?

[wsxdrfv]

If user A send coin to some address B, if that transaction has 0 confirmed, what happen that coin?

He lose money? or how he restore money?

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[TryNinja]

It takes some time to get your transaction confirmed in the blockchain. When it gets at least 1 confirmation, the user B will be able to spend the coins. If the transaction never gets confirmed, the transaction will be dropped from the mempool after a few days and the coins will "come back" to user's A wallet, where he will be able to spend them again.

[ranochigo]

No. The transaction will appear in the mempool till the individual nodes decides to remove it or if it gets mined. The transaction does not simply disappear; its either you "get" your coins back or it gets confirmed.

In the event that the unconfirmed transaction stays in the mempool of a node for too long, the node can decide to remove the transaction from its mempool. If you're using Bitcoin Core, your transaction should disappear the same time as the other nodes. When this happens, it would be as if the UTXO has never been spent. If you don't want your transaction to be dropped, simply rebroadcast it (some clients do this automatically).

[Xynerise]

If user A send coin to some address B, if that transaction has 0 confirmed, what happen that coin?

He lose money? or how he restore money?

Technically, as long as the transaction has not been included in the blockchain, the UTXOs that transaction spends still belongs to the original sender, and s/he can spend them in another transaction.
This breaks no consensus rules because the transaction has not been mined yet, and so is not in the blockchain.

[paul gatt]

In my opinion if you send money to someone whose transaction is not confirmed, you will not lose money. Please check the account of both. If your account has been charged, the other party has not yet received it. Keep that calm due to errors to confirm the account information. I have met this case.

[vit05]

It takes some time to get your transaction confirmed in the blockchain. When it gets at least 1 confirmation, the user B will be able to spend the coins. If the transaction never gets confirmed, the transaction will be dropped from the mempool after a few days and the coins will "come back" to user's A wallet, where he will be able to spend them again.

But is it not possible, although rare these days, to receive and use a coin, after the transaction has no confirmations? It is insecure. But I remember some discussions where zero confirmation transactions were still possible.

There is some currency, such as nano, which is based on something similar to that. There is even some exchange that operates BCH like that. Leaving transactions virtually instantaneous. It is very unsafe and risky. Maybe stupid. But it's a possibility.

[Ray55]

In this blockchain technology if sender A transfer his/ her coin to B and the transaction not get succeed  then the coin come back to the sender after few days  and it  will be original . Don't  afraid . Because if the transaction failed , it takes some time to back in the senders  wallet as the original one.

[TryNinja]

But is it not possible, although rare these days, to receive and use a coin, after the transaction has no confirmations? It is insecure. But I remember some discussions where zero confirmation transactions were still possible.

There is some currency, such as nano, which is based on something similar to that. There is even some exchange that operates BCH like that. Leaving transactions virtually instantaneous. It is very unsafe and risky. Maybe stupid. But it's a possibility.

Yes. You can spend unconfirmed coins (i.e Electrum has this option). But the transaction will only get confirmed once the previous ones does aswell.

[bob123]

There is some currency, such as nano, which is based on something similar to that.

Nano utilizes a directed acyclic graph. This is not similar to blockchain technology.
In a DAG-based currency people are simply adding transaction to the graph 'whenever they want to'.
Compared to blockchain currencies (where transactions get confirmed by miner who do a PoW to create a block) this is a completely different approach.

While it has the advantage of faster transactions ('confirmations') it is way more vulnerable to DoS attacks.
Additionally the security of all those DAG-based currencies havn't been tested yet. While Bitcoin (blockchain tech itself) has been attacked for several years now - without success.

[hatshepsut93]

2. If the transaction never confirmed (simply dropped by miners/nodes after few days), the coin isn't lost and the coin "come back" to sender.

When you broadcast a transaction, all or almost all full nodes of the network will put it into their mempools and they will by default refuse to broadcast any transactions that try to spend the same coin, unless it's RBF transaction. What you are describing as "coming back" is a mempool eviction, after some time nodes may start to remove stuck transactions from their mempool, so technically you can try to broadcast it again and there's some chance that a new transaction will reach miners. However, some nodes might for some reason also broadcast your old transaction, so it might linger in mempools for a really long time. I've personally had a transaction get stuck for more than 6 weeks until it got confirmed, due to very low fees (this was when we had ~$30 fees).

[MrCrank]

If user A send coin to some address B, if that transaction has 0 confirmed, what happen that coin?

He lose money? or how he restore money?

In any case need wait confirmation TX.
Can't answer to your questions. because 3 way: confirmed, returned, doublespend