Thanks for reaching out to the Zoom Developer Forum, I am happy to help here!
There are some steps that might help you to debug your issue:
Send a post request to your Endpoint URL, if you do not receive this event then you will have to check your Endpoint
If you DO RECEIVE the post request, but not the Zoom events, try replacing your endpoint with a test endpoint of your preference (such as webhook.site).
If you receive events and Zoom events in this test endpoint, please check that your Endpoint URL is working properly.