Reverse Engineer Calculation Fix Needed

I already have a compiled app in production, but one core routine is returning the wrong numbers. I no longer have reliable source code, so this will involve classic reverse-engineering: decompiling, analysing the existing logic, correcting the calculation errors, and rebuilding a clean, working binary.

The only change I need is a bug fix—specifically for calculations that currently produce incorrect results. No new screens, flows, or cosmetic tweaks are required. After your patch, the app must display and store the right figures under every scenario we can throw at it.

You are free to use whatever toolkit you prefer—IDA, Ghidra, Hopper, Frida, etc.—as long as the final deliverable is:

• A rebuilt executable with the calculation bug resolved
• A short technical note outlining what was wrong and how you fixed it (enough for future maintenance)

Once I verify that all test cases now return accurate data, we can wrap the job.