EventGrid Subscription Webhook validation handshake failure

Question

I am setting up a new project where I need to setup EventGrid Topic subscription pointing to an API url of my Development API Management instance which is internal only. It uses commercial CA certificates as advised in here. I am getting following error when I try to create a subscription through terraform. I feel it is not able to reach the internal only url as the policy is set in APIM to validate the SubscriptionValidation POST request. I am able to test the APIM API policy by sending a POST request from my pc connected to internal network.

Is my assumption correct that we need to make our APIM instance external or is there any other way where I can still validate the url keeping APIM instance internal only?
Status: "Failed"

│ Code: "Url validation"

│Message: "Webhook validation handshake failed for https://my-dev-apim-url/api Http POST request failed with response code Unknown. For troubleshooting, visit https://aka.ms/esvalidation.

Answer 1

@Prajnan Kotoky Thanks for reaching out. Based on the error message you provided, it seems like the Event Grid Topic subscription is failing to validate the webhook URL for your Development API Management instance.It is possible that the issue is related to the fact that your API Management instance is internal only and is not accessible from outside your network.

consider exposing your APIM instance externally to resolve this issue.

do let me know incase of further queries, I would be happy to assist you.