## TL;DR

That is what turns the call into an upsert; without it you get plain inserts and every rerun duplicates the table. Pick columns whose values are unique and never change, like an external record ID, not a display name.

## Steps

1. When you sync data into Coda with upsertRows, always include keyColumns naming the stable identifier columns. That is what turns the call into an upsert; without it you get plain inserts and every rerun duplicates the table. Pick columns whose values are unique and never change, like an external record ID, not a display name.

## When to use

You are seeing this: When you sync data into Coda with upsertRows, always include keyColumns naming the stable identifier columns. Use this skill when you run into "Coda API upsertRows: pass keyColumns or every sync creates duplicates".

## When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

## Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

## Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.