Unabashed plug for GnuCash. It's FOSS, double-entry, and capable enough for oddball personal finances or business finance, with all the spreadsheet exporting one might need.
I get the idea. But the way it was written has a "I heard from a guy who did a thing that looked like this..."
Maybe it's written that way to protect the privacy/trade secrets. But it also makes it hard to have any takeaways beyond why a dev team approved of pushing code like this to prod with minimal testing.
That's a process error, not an individual's fault. Sounds like not a single person reviewed the code, they just said, "sounds good, deploy!" on a major production system.
You can be certain that there are tons of other bugs in the system that just have more subtle effects.