phone:write API key. Resolve contactId from the signed-in customer and choose an authorized destination: either { type: 'agent', id } or { type: 'team', id }.
Reuse the UUID requestId for identical retries until activation. Changed settings or retries after activation return 409. maxDurationSeconds defaults to 1800 and accepts integers from 60 to 3600; the duration starts at activation.
A successful response is HTTP 200 with the credentials consumed by the SDK. Join and activate within two minutes. expiresAt is the outer call-control deadline, not an extension of that join window. Credentials must be returned only to the authenticated customer and must not be logged or cached.
Creation returns 400 for invalid settings or unsupported agent transfers, 401 for invalid authentication, 403 for missing scope or preview access or a blocked contact, 404 for an unavailable contact/destination, 409 for conflicting or active calls, and 429 when requests are throttled.