Run bulk call campaigns entirely over the API

The public API now covers the full bulk-calling lifecycle: create a campaign with the same settings the dashboard offers, add thousands of contacts in one request, start it, adjust concurrency, retry failed calls, and page through results with a cursor that never skips a contact, even on campaigns with hundreds of thousands of rows.

Number rotation is included: define a pool of caller numbers at campaign create, then read and steer the rotation over the API while the campaign runs.

Guides and examples are live in the docs.