The Coldcard Mk 3 hardware device is compatible with Casa Multisig.
Whether you are adding the Coldcard, doing a health check, or sending funds from your Casa multisig keyset, it has the unique benefit of offering offline-signing via PSBT's to add a signature to your keyset.
One thing to keep in mind when using your Coldcard is to remember to check for the most recent firmware updates here.
With Coldcard, the instructions for performing a health check and signing a transaction do differ slightly. See the below articles for the instructions for each function:
Some common Coldcard errors are:
"Failure. My XFP not involved"
Solution: Double-check that the SD card and Coldcard are the devices used for that keyset. If you are performing a key rotation make sure that you are using the device you marked for replacement to essentially give permission to transfer funds to your new keyset.
There is an issue with the Coldcard firmware where it looks for the OP_CHECKMULTISIG opcode in the redeem script, but can't find it because it isn't taking into account that we use nested segwit (P2SH-P2WSH). It's assuming all addresses are P2SH or P2WSH.
You can get around this by going to Settings > Multisig Wallets > Skip Checks, and turning that setting on.
"Couldn't find signature"
Solution: Make sure to upload the correct file to confirm this request. It will prompt you with the file name to look for in the error message.
"Failure Invalid PSBT multisig.py 716"
This is shown when trying to sign a testnet transaction, but the right setting has not been configured. In order to sign for testnet you must do the following:
In Coldcard settings, select: Advanced > Danger Zone > Have ‘Testnet: BTC’ checked, not ‘Bitcoin’
"Failure XPUBs in PSBT do not match any known wallet"
This is shown if "Trust PSBT" is not enabled.
In Coldcard settings, select Multisig Wallets > Trust PSBT and select "Trust PSBT."
If you've tried the above steps and are still having issues, please reach out to our support team, and we're happy to assist.