Resource Webhook not working

I've been unable to get a resource webhook to fire.

The initial verification request was successful.

When creating the web hook I set

"scope": "RESOURCE"

subscribed to AGREEMENT_ALL

set the resourceId to an agreement id.

"resourceType" : "AGREEMENT"

"state" : "ACTIVE"

I can view the webhook from the adobe sign admin web app under the "Webhooks" tab. The status is active.

On signing or performing any other action against the agreement the web hook is never called and, as far as I can tell, no attempts are being made to call the web hook.

If I manually create an ACCOUNT webhook, this works fine with agreement actions are triggering calls to the web hook. NB I've deleted the web hook I created manually.

Any ideas as to what I missing would be greatly appreciated?