Signing a Transaction With Coldcard

After adding your Coldcard to Casa App, you can use your Coldcard to sign a transaction, or perform a health check on the device. 
 
The steps detailed below to sign a transaction from your keyset. 
 
If you haven’t added your Coldcard to Casa yet, please see our article Adding Coldcard to Casa App.
 
If you want to learn how to perform a health check, see Performing a Health Check with Coldcard.
 
When signing a transaction, you will need:
 
        - Coldcard device
        - A laptop or desktop computer
        - Micro SD card 
        - Micro SD card adapter (if your computer does not have a micro SD card slot)
 
First, initiate a transaction from within Casa App.
 
Note: Coldcard has a default setting where it will not sign transactions if the fee is set as more than 10% of the transaction. This is to prevent accidentally sending a transaction with a larger fee than intended, but can be an issue if you're attempting to sign smaller outgoing transactions. You can disable this default setting if needed by following Coldcard's instructions here (see section on "Max Network Fee).
 
Next, check your email inbox for an email from Casa with a link. Clicking that link will initiate the signing process.
 
Physically insert your SD card into your computer (you may need an adapter for this step). 
 
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When you click the link, you’ll be prompted to download a .psbt file onto your computer. Once the file is downloaded, drag and drop the file onto the Coldcard’s SD card.
 
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Next, take the SD card out of your computer and insert it into your Coldcard.
 
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When your Coldcard is powered up and unlocked with your PIN code, click the "checkmark" button to select Ready To Sign
 
If there is only one .psbt file on the Coldcard, it will immediately begin the transaction verification and signing process. If there are multiple files then you will need to select which one to sign.
 
Once you finish verifying the transaction details, the Coldcard will save the signed psbt to the SD card.
 
Now that the transaction’s signature is copied to the SD card, you’re ready to transfer the signature back to your computer to complete the signing process. 
 
Remove the SD card from the Coldcard and insert it into your computer. 
 
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Back at the Casa API, click “Next,” then drag and drop the file ending in "-part.psbt" into the window when prompted.
 
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We recommend deleting the -part.psbt file from the MicroSD once finished uploading.

 
That’s it!
 
If you’re signing a transaction, you’ll need to give your other signatures to the transaction, if necessary, and complete the transaction from within Casa App.

 

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