Hi @Ksheva, 

We use OAuth to authorize API requests. It sounds like the OAuth access token is not being passed correctly to the /webhook_subscriptions endpoint.

There are two ways to get an access token:

• Creating an OAuth app and authorizing access to that app. More details here: https://developer.calendly.com/api-docs/3cefb59b832eb-calendly-o-auth-2-0
• Creating a personal access token (PAT) on the Calendly integrations page: https://calendly.com/integrations/api_webhooks

Have you done either of those steps first? If so, can you reply with the HTTP headers for the request that you’re making (with the token omitted).

-andrew