Why is the URI of an Azure runbook webhook URI blank - azure

Question

I am using an ARM template to deploy a logic app in a second subscription in Azure which needs to trigger a POST to a webhook URL of a runbook in the first subscription.
I use the full reference to the webhook URL object in the ARM template, but unforuntately although there is no error, the logic app ends up with a blank URI.
The reference to the webhook looks like:
"RunbookWebHook": {
"type": "string",
"defaultValue": "/subscriptions/----/resourceGroups/RunbookResources/providers/Microsoft.Automation/automationAccounts/RunbookAutomationAccount/webhooks/RunbookWebhook"
},
An example reference to the webhook URI in the logic app:
"actions": {
"Runbook_Webhook": {
"runAfter": {},
"type": "Http",
"inputs": {
"headers": {
"operationName": "#{triggerBody()['data']['operationName']}",
"resourceId": "#triggerBody()?['subject']"
},
"method": "POST",
"uri": "[reference(parameters('RunbookWebHook'), '2015-10-31').uri]"
}
}
How can I get the correct URL for the webhook URI?

Answer 1

This is because of a restriction in Azure with regards to the Webhook URL.
In the MicroSoft documentation: https://learn.microsoft.com/en-us/azure/automation/automation-webhooks#webhook-properties
it mentions the URL property (which is actually the uri field) and it says:
URL of the webhook. This is the unique address that a client calls with an HTTP POST to start the runbook linked to the webhook. It's automatically generated when you create the webhook. You can't specify a custom URL.
The URL contains a security token that allows a third-party system to invoke the runbook with no further authentication. For this reason, you should treat the URL like a password. For security reasons, you can only view the URL in the Azure portal when creating the webhook. Note the URL in a secure location for future use.
So the URL cannot be further retrieved after creation. :(