How to get a callback when an Azure Marketplace Managed Application is installed from marketplace

The Microsoft documentation states:

Provide a notification endpoint URL: In the Notification Endpoint URL box, provide an HTTPS Webhook endpoint to receive notifications about all CRUD operations on managed application instances of this plan version.

I created a simple Logic App and copied the HTTP endpoint into my MPN App Plan under the

It looks like this and has the sig at the end:

https://prod-08.australiaeast.logic.azure.com:443/workflows/fe287d1b9a8c48619a1b44765dad6dc7/triggers/manual/paths/invoke?api-version=2016-10-01&sp=%2Ftriggers%2Fmanual%2Frun&sv=1.0&sig=C9JYfNPjvq-efsLwW66A4K4zTgx6qxGT1oH0RZZRsI0

To test it I hit it with PostMan and confirm that it is getting an HTTP200 as per the MS Docs.

I publish the app to the marketplace:

(you can see the app live here - https://azuremarketplace.microsoft.com/en-us/marketplace/apps/data-drivenai1581501556049.cloudmonitor-analytics-engine)

However - the endpoint never gets called at all. I can see in the logs that no attempt (failed or past) has been made to call it.

I raised a Microsoft Support Ticket and asked a Technical Specialist, however no one can tell me how to debug it or why it is not calling back on installs or failed installs.

Has anyone seen this working?

Update I found out that each PLAN has a GUID that is automatically used for deployment. Mine is "pid-34881ea9-xxxx--xxxx-xxxx-2cf731e06ef7-partnercenter" - should I be putting this on the callback notification URL as sig=ThisGUID?

In the example for Managed apps with notifications, it shows that managed applications will send a post to https://{your_endpoint_URI}/resource. Can you try adding /resource to your listener and see if it triggers your logic app? I believe that should fix this.