Registers an HTTPS URL to receive event deliveries. The URL is
ping-verified synchronously; creation fails with 400 if the
receiver does not respond 2xx within 5 seconds.
The response includes secret, a 64-char hex string used for HMAC
signature verification. It is returned only once.
OptimalDial API key, prefixed od_live_, sent as Authorization: Bearer ....
Mint keys in the in-app developer panel; they are scoped to a single organization.