Unable to create webhook subscription, receiving 400 status code

If you attempting to create a webhook subscription via the [RingCentral Subscription API][1] and are receiving a 400 HTTP status code, then chances are one of two things is going wrong. **Properly validate the webhook URL** When you subscribe to an event via a webhook, RingCentral will attempt to validate the URL you specify in your subscription request. This validation step requires your application to respond to an incoming validation request in a prescribed way. Please consult our documentation on "[validating webhook URLs upon subscription creation](https://developers.ringcentral.com/guide/notifications/webhooks/creating-webhooks#Validating%20webhook%20URLs%20upon%20subscription%20creation)". **Ensure your webhook URL meets all requirements** From the [RingCentral Developer Guide][2]: > When you create a webhook subscription, RingCentral will transmit a test request to the designated URL in an attempt to verify all of the following prior to creating the subscription and transmitting events. > > - The URL must accessible by RingCentral and not behind a firewall > - The web server supports TLS 1.2 or higher (see note below about TLS support) > - The web server must respond within 3000 milliseconds > - The web server must respond with an HTTP status code of 200 OK > - The web server must respond with a valid Validation-Token header **Call the Subscription API correctly** It is important to rule out the possibility that you are unknowingly calling the Subscription API incorrectly. To rule this out, try creating a subscription via a [simple demo application](https://ringcentral-subscription.herokuapp.com/login). If you are successful in creating a subscription using this demo app, then the most likely reason you are receiving an error is because you are not formatting your request properly. [1]: https://developers.ringcentral.com/api-reference/Subscriptions/createSubscription [2]: https://developers.ringcentral.com/guide/notifications/webhooks/creating-webhooks