Firmware version B-2.0 (BTC-Only) or newer allows you to use Casa V 3.6.0 or newer with your Keystone Essential or Pro hardware wallets. Detailed instructions provided below explains how to directly interact with Casa to create a 2-out-of-3 multi-signature wallet between your Keystone hardware wallet, Casa's Mobile Key and Casa's Recovery Key as the 3 participant co-signers. This tutorial also explains how to execute a 2-out-of-3 multisig transaction.