Make it explain the spreadsheet formula before it fixes it

Spreadsheet formulas are one of the best things to hand an AI, and also where people paste in something they can't read and hope. Explain first, then fix, then test.

Here's a spreadsheet formula and what I want it to do.
Product and version: [EXCEL 365 / EXCEL 2016 / GOOGLE SHEETS]
Formula: [PASTE]
Layout: column A is [WHAT], column B is [WHAT], my data starts at row [N].
Goal: [IN PLAIN ENGLISH].
Step 1: explain what the formula does now, part by part, in plain
English.
Step 2: say why it doesn't do what I want.
Step 3: give me the corrected formula and explain what you changed.
Step 4: give me three test rows (including one blank and one odd value)
with the result you expect for each, so I can check it.

The explanation is where you find the misunderstanding. Often it's the first time you've seen what your formula was really doing.

The layout line is so it doesn't invent column letters (it will, and you'll lose ten minutes working out which one it made up). The product and version line matters because newer Excel functions don't exist in older versions, and Sheets does its own thing again.

The test rows are the safety net. A formula that works on the happy path and falls over on a blank cell is the classic.

Don't paste real customer or staff data. Make up three rows with the same shape.