# An Idempotency-Key header is required

> 400 idempotency_key_required

Placing a call needs your own id for it in the `Idempotency-Key` header, so a retry never calls anybody twice.

## What to do

Send an id built from your own data, like `lead-8812-attempt-2`, up to 120 characters.

## Retrying

No: the same request gets the same answer until something is changed.