Webhook validation failures even though it validates through the UI

API Endpoint(s) and/or Zoom API Event(s)

I have created webooks with event subscriptions, successfully validated them and successfully received callbacks.
But now I am getting an email that says “Action Required… Your webhook endpoint failed to respond to our validation request. If your webhook endpoint fails to respond to our validation requests 2 more times, we will stop sending webhooks to your webhook endpoint until you fix the issue.”

But my webhook is working.

If I create another identical webhook by clicking the blue Add Event Subscription button, paste in the same url, and click Validate i see a green tick that says my webhook is validated ok.

I don’t understand why I’m getting the email messages saying my webhook is failing to validate… There are no logs on the Zoom side where i can check if there is an error message. Whe I look at my server logs I see a POST from zoom to my webhook endpoint that gets a 200 response, and a second one 3 minutes later. Both appear valid.

What should I do?

thanks
Steve