The missing step is likely app authorization, not the scopes. Endpoint validation only confirms that Zoom can complete the URL challenge. A General app must also be installed through Local Test → Add App Now. After changing scopes or webhook settings, authorize the app again before running a new test meeting.
Once the app is authorized, create a new cloud-recorded meeting and wait until the transcript finishes processing. Existing transcripts created before authorization won’t retroactively generate the webhook.
Recall.ai’s Meeting Bot API can also manage Zoom meeting recording and transcript workflows.