When A sends money to B both have an expectation that B is able to access such money through normal monetary systems like: seeing their bank balance go up, withdraw it as cash, or transfer it again to C which will have a similar recursive set of expectations.

Unless your database is the de facto central banck for the currency A and B use you will have to convice B's monetary system to believe B now has more money. The simples and almost only way to do that is to pay the appropriate price in a currency they like.

Which requires liquidity.

As an example if you wanted to install a bitcoin ATM with withdrawl* in a train station (or anywhere else) you would need liquidity in whatever currency the user want to withdraw.

* I suppose you could withdrawn bitcoin by giving out fresh wallets with the sum or by simply transfering it.