I’m looking for software similar to what Venmo would use, but not sure where to start

Im looking to make an app/service that is similar to Venmo, and im not too technical, so seeking some input on what the software basically is.

The functionalities of the app seem pretty simple, but I’m not sure where to start. They seem to have just a secure internal ledger with user accounts, that allow the users with accounts to send some of their balance to other users. Is this technically just some sort of database? How complicated is developing something like this, or is there anything out there already made for this?

I have seen several different pieces of software that companies have built for money service businesses, but they all seem to have much more features than needed, and very highly priced. But the functionalities needed for just having user accounts with different balances doesn’t seem too complicated to me.

I appreciate any help or input, thanks 😁