Petit test
Guess first, no penalty. You ask AI for a formula to total March travel costs. It gives =SUMIFS(C2:C400, A2:A400, "March", B2:B400, "Travel"). Your data runs to row 500. What happens?
A formula is the instruction in a spreadsheet cell that calculates a result. AI writes them well, including SUMIFS (adds up the numbers that match your conditions) and XLOOKUP (finds a value in a table).
But the tool can't see your file. It guesses the ranges, the sheet names and how your dates are stored. And a wrong formula rarely shows an error. It shows a wrong number that looks fine.
So do two things. Tell it your exact layout. Then test the formula on a few rows you can add up yourself: filter to March and Travel, add three or four rows by hand, and compare.