Transferring, backing up, and redeeming Cashu essentially involves dealing with a "Mint." The balance in your hands is a string of secret keys known only to you. Whether you can get your money back depends on two things: whether you have backed up your seed phrase, and whether the Mint you use is still operating normally.
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Below is a guide based on what you actually need to do.
Transfer: How to Send Cashu
A Cashu transfer is not an on-chain transaction, nor is it a Lightning transfer. What you send to the other party is a string of tokens. The recipient takes this string to a Mint to redeem it, and only then do they actually receive the money.
In most Cashu wallets (such as PWAs or apps like Cashu.me), the sending process is basically the same:
Select the amount to generate a token.
Copy the token string or display the QR code and send it to the other party.
The recipient selects "Receive" in their wallet and pastes the token or scans the code.
There is a key difference here: the moment you click "Send," the Mint does not automatically transfer the token from your balance to the recipient's name. In reality, your wallet first initiates a "swap" operation with your selected Mint. It splits out the amount you want to send, generates new blind-signed tokens for you, and marks the old proofs as spent. The token string you receive is the encoded form of the newly split proofs.
Therefore, whether a transfer succeeds depends on whether the recipient redeems it at the same Mint. If the recipient's wallet does not have the Mint you used, they will need to add that Mint before they can redeem. The wallet will usually parse the Mint address from the token. If the recipient's wallet does not support this Mint, it will simply show an error.
If you send a token to someone who does not plan to redeem it immediately, the token itself will not expire, but the Mint may deactivate the old keyset at some point in the future. Once a keyset is deactivated, old proofs may not be redeemable directly, and the Mint may need to provide a migration or redemption channel.
If you just want to transfer to another wallet you control, an easier approach is to import your seed phrase into the new wallet. The new wallet can restore the balance directly from the Mint, so you do not need to generate a token and receive it again.
Backup: The Seed Phrase Is the Only Thing You Really Need to Keep Safe
Backing up a Cashu wallet is not exporting a screenshot of your balance, nor is it saving token strings. What you really need to back up is the 12-word (or 24-word) seed phrase.
Starting from NUT-13, the Cashu protocol supports deterministic derivation. The wallet uses the seed phrase as the root key and, following an incrementing counter, derives the corresponding secret and blinding factor for each newly minted token. This means that as long as you have the seed phrase and know which Mints you used, you can theoretically re-derive all previously minted tokens, then query the Mint to see which ones are still unspent and restore your balance.
Conditions for recovery:
The Mint must still be online and still retain the corresponding keyset to handle recovery requests.
The recovery process involves batch scanning on the Mint's /restore endpoint. It may take a few minutes, depending on the number of keysets and transactions you have used.
Recovery only works for tokens minted after the seed phrase was enabled. If you already held some tokens before enabling seed phrase backup in your wallet, those old tokens were generated with random secrets and cannot be recovered from the seed phrase, unless you proactively do a "self-transfer" after enabling backup to convert your entire balance to the new format.
Do not use the same seed phrase in multiple wallets at the same time. NUT-13 derivation depends on a counter. If two wallets each maintain their own counter and are used simultaneously, the derived secrets will conflict, potentially causing "token already spent" errors or inconsistent balances. If you restore on a new device, do not continue using the same seed phrase on the old device after the restore is complete.
Redemption: Converting Ecash to Lightning or Withdrawing to an Exchange
In the Cashu context, "redemption" usually refers to melting: you hand your ecash to the Mint, and the Mint pays the equivalent amount of satoshi to your specified address via the Lightning network (or pays a Lightning invoice for you).
Steps:
In the wallet, select "Pay Lightning Invoice" or "Withdraw to Lightning Address."
The wallet requests a melt quote from the Mint, and the Mint returns the required fee (if any).
After you confirm, the Mint accepts your proofs and initiates the payment on the Lightning network.
The most easily overlooked point here: whether a melt succeeds depends on the status of the Mint's Lightning node. If the Mint's node has insufficient liquidity or a routing failure, the payment may get stuck. The Mint usually has a timeout window. After a timeout, the proofs may be returned, or you may need to actively trigger a status sync to recover them. If the Mint itself disappears or goes offline, the melt cannot be completed.
If you want to withdraw to a centralized exchange, the process is the same as a normal Lightning withdrawal: generate a Lightning invoice on the exchange, then pay that invoice in your Cashu wallet. The exchange receives a normal Lightning deposit and will not know the funds came from Cashu. But note: the exchange may have risk controls on deposit sources. That is a separate issue and has nothing to do with Cashu itself.
What to Do When Stuck or Seeing Errors
The two most common errors are "Already Spent" and "outputs have already been signed before". These usually mean the local proof state in your wallet is inconsistent with the Mint's records—either the counter was not aligned during recovery, or the same proof was used twice.
Handle it in this order:
First, sync the proof state. Look for "Sync Balance" or a similar function in the wallet. This makes the wallet query the Mint for the current status of each proof (unspent / spent / pending) and update the local records.
If the error persists after syncing, try bumping the counter. In the ZEUS wallet, the path is
Menu > Tools > Cashu Tools. Increase the counter a few times to force the wallet to skip derivation positions that may have conflicts.The last resort is to remove the Mint and add it again. When removing, first copy the Mint URL. After re-adding, check "Check existing balance" so the wallet rescans and restores from the Mint. This process may be slow.
If none of the above works, export your seed phrase from the wallet and import it into another Cashu wallet (such as Cashu.me) to try recovery from a different implementation. But this only works if the Mint is still online.
There Are Only Two Things You Really Need to Watch
The reputation and survival status of the Mint. Cashu ecash is custodial—the Mint controls the backing Bitcoin, and what you hold is only an IOU from the Mint. If the Mint shuts down, disappears, or deactivates a keyset without providing a migration window, your ecash could become an unredeemable IOU. This is not a protocol flaw; it is the inherent cost of the custodial model.
The seed phrase. Assuming the Mint is still online, the seed phrase is your only proof for recovering your balance. A screenshot of your balance or a saved token string cannot replace the seed phrase. If you are using a Cashu wallet that does not provide seed phrase backup, you should seriously consider whether to keep your balance in it.
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References
- ZEUS Documentation·Cashu ecash, page undated; checked on 2026-10-12.
- cashubtc/cdk·Restoration and Recovery, page undated; checked on 2026-10-12.
- cashubtc/nuts·Release 0.13.0 – Ecash backups, page published or updated on 2023-07-25; checked on 2026-10-12.
- Cashu Protocol·NUT-13: Deterministic Secrets, page undated; checked on 2026-10-12.
- GitHub·Cashu eCash Integration (SatSigner), page undated; checked on 2026-10-12.
- Stacker News·reply on: Stay away from Voltz, page published or updated on 2025-02-09; checked on 2026-10-12.
- KuCoin·Cashu Protocol Explained, page published or updated on 2025-12-24; checked on 2026-10-12.
