Errors
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.