Digital money requires a ledger. By integrating this ledger with its other ledgers, a platform can enforce repayment of uncollateralized credit, beyond the ability of the banking sector. However, by controlling interoperability to other platforms' ledgers, an incumbent platform can ``lock-in'' customers and increase its market power. Open banking, which gives users control of interoperability, limits uncollateralized credit. Introducing CBDC as digital legal tender (on an isolated ledger) hurts credit extension, but enhances it when combined with an open architecture public ledger as a ``smart CBDC''.