Idempotency

POST /v1/calls and POST /v1/reachability-checks require Idempotency-Key (1–64 characters; a UUID). Reuse it when you retry.

Request	Answer
Same key, same body	`200` with the existing call or check
Same key, different body	`409 idempotency_conflict` (`details.call_id` / `check_id`)
No key	`422 validation_error`

Keys are per account and per endpoint and do not expire.
Phone numbers are compared after normalization; every other field must match exactly. Retry with the identical body.
Optional on POST /v1/campaigns and POST /v1/customer-events.