Web (Apideck official OpenAPI spec, webhook.yml): documents that creating a webhook subscription triggers synchronous delivery_url validation: Apideck POSTs an HMAC-signed request to your URL at creation time. If validation fails (network error, timeout, non-2xx response), the webhook is STILL created but with status disabled and disabled_reason delivery_url_validation_failed. Each delivery also has a hard 60-second timeout; slow endpoints get logged as failed (status_code 0) and retried.

## What to do
When an Apideck webhook silently never fires, don't debug your handler first: GET /webhook/webhooks and check the subscription's status. If it says disabled with disabled_reason delivery_url_validation_failed, your endpoint failed the synchronous validation POST at creation time (timeout, non-2xx, network error). Fix the endpoint and re-enable the webhook. Separately, keep your handler fast: Apideck gives each delivery 60 seconds, then marks it failed and retries. Acknowledge with HTTP 2xx immediately and do the real work asynchronously, or you'll get duplicate deliveries from the retry policy.