In this video you will see the usage of PSBT, watch-only wallets. And how to send transactions offline with your Coldcard and Bluewallet. Using dropbox on this example.
- Start the Coldcard device, go to Advanced → MicroSD Card → Export Wallet → Electrum Wallet. Put the SD card into Coldcard. Choose Native Segwit. It should create wallet skeleton file on SD card.
- Put the SD card into the PC and move the created wallet skeleton file onto the Dropbox folder.
- Grab the iPhone, launch BlueWallet, tap Create a wallet → Import wallet → scan QR or import from file → tap file icon and choose your wallet skeleton file. It should import your Coldcard wallet as watch-only.
- Create a transaction from this watch-only wallet, when prompted - export it to a file and save it in Dropbox folder.
- Put the SD card back into the PC, and move the transaction file from Dropbox folder to the SD card.
- Put the SD card into the Coldcard, go to Ready To Sign and proceed with signing the transaction.
- Put the SD card into the PC. There should be 2 new files: a file with tge transaction hex that is ready to broadcast (*-final.txn), and a signed transaction file (*-signed.psbt).Let us finish the transaction on iPhone, so move signed transaction file to Dropbox.
- On the iPhone, tap Open Signed Transaction, and choose the signed transaction file from your Dropbox. Tap Send now!
PS: Take in consideration that we used dropbox on this example, but anything will work, File system, iCloud, Bluetooth, AirDrop, box.com, direct lightning to sd card adapter, etc