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I created an Electrum Cold Storage Wallet (CSW) on an offline Win 7 laptop, copied the Master Public Key (MPK) & used it to create a standard Watching Only Wallet (WOW) on an online macOS computer. I sent Bitcoin to the WOW & setup a test transaction of 0.0002 BTC to send to the CSW, I saved the transaction to a USB stick but the file extension is .psbt. I tried opening the file for signing on the CSW but got "No items match your search" as a .txn file was expected.

Maybe creating a standard wallet with the CSW seed would solve the problem but at the cost of exposing the seed to the internet. I didn't create a Multisig wallet so I don't know what happened, what is the best way forward?
 ???
Electrum 4.5.4
macOS Sonoma 14.4.1

No the .psbt file is what is needed. You just need to find it. Go to tools, then load transaction file, look for any file of .psbt. Sometimes when you use the direct search button with file name I think it doesn’t work.

You can as well decide to update to a higher windows version like windows 10. You should also try to make sure that the electrum wallet version on both airgapped device and the online one is same


No you don’t create a watch only wallet with a seed phrase or private key, it is not longer a watch only wallet again. You create it with address or master public key.

The cold wallet is also a standard wallet but offline and not online which makes the difference. It is better the way you did it. Follow what Zaguru12 first quote and post and you will get it. Electrum will take you to the .pbst file directly in a way you can click on it to broadcast the transaction. If that is difficult for you, you can use QR code instead which is even better.

Electrum is not supporting lower version than Windows 10. Electrum version on airgapped and watch-only device do not have to be the same update version, most people do not like to update the cold wallet because they want to keep it out of external environment data aside PBST transactions, but updating the watch-only.

Yes that's probably what it is, the Electrum CSW is ver.3.2.3. I need to upgrade everything, thanks. 8)

Starting from version 4.0.1, you will not have the issue to sign PBST, but the lower version starting from 3.3.8 has different PBST singing format which is the reason for the issue you are having. If that is what that it is, you will need to update to lastest version. That is right.

But there is no yet any changes in the PBST signing since version 4.0.1 till now. So you do not need to update the cold wallet often. Keep the device offline as possible and also keep it away from external data transfer if possible, unless in case of issue like this arise again in the future.

Yeah when OP said he uses windows 7 I thought he was using a lower Version of the electrum wallet since from the version 4.2.0 the support for windows 7 was stopped. Also he included that the watch only wallet was on version 4.5.4 that’s why I asked him to update the airgapped wallet to the latest version or more recent one, as I once read that a older version of electrum isn’t not compatible sometimes with the exported file from the new one.

 

Glad it helped but make sure you’re upgrading the wallet properly do not make a mistake or bring that device online. You can simply down the binaries for electrum wallet, verify it, all on another device and then transfer to the cold wallet using any offline method.

After upgrade you could also try the QR-Code signing format I think it's quite easy as you won't be needing a usb-stick to save your transaction  file, just your pc cam to scan your QR-Code will be needed and you can scan again to broadcast transaction.
Easy!! No stress.....

Updating the cold storage is not necessary in my opinion. Only few updates are needed. Since version 4.0.1, the update is not needed till now.

Exactly. QR code is the best way to avoid malware. It is easier, simpler and faster.