Automate interview scheduling with the Calendly API and sync confirmed slots back into an ATS

Steps

1. Authenticate with a personal access token or OAuth 2.0 application, and confirm the Calendly plan (Standard/Professional/Teams/Enterprise) and paid host seats are in place, since org-wide access and webhooks require a paid plan
2. Create a webhook subscription for invitee.created (and invitee.canceled) events, specifying the callback URL, the events array, the organization URI, and — if scoping to a single user rather than the whole org — that user's URI
3. When sending a candidate a booking link, embed an ATS-identifying tracking value (e.g., via a custom question answer or link parameter) so the webhook payload can later be matched to the correct ATS record
4. On receiving invitee.created, verify the webhook signature, extract interview date/time, interviewer, event type, and candidate-provided answers, then write the confirmed slot into the ATS via the ATS's own interview/candidate API
5. Handle invitee.canceled the same way to clear or flag the previously synced interview slot in the ATS
6. For fully embedded scheduling without a Calendly-hosted UI or redirect, use the newer Scheduling API's Create Event Invitee endpoint to book on the candidate's behalf directly from the ATS interface