@Bertha Chavez Thanks for reaching out. The error is expected as you need to perform the endpoint validation and for more details you can refer to this document.
When you create the event grid subscription so the first event will be validation event and your webhook endpoint needs to perform the validation, so the event grid subscription is created sucessfully.
Once I have started ngrok you can see the web interface and forwarding. The forwarding endpoint (over the internet) will be your webhook endpoint that you will be configuring while creating the event grid subscription. In the web interface you will see the validation code and URL as below.
Get the validationUrl and open the URL in your browser so the validation of endpoint is sucessfull.
Successfully Validating the endpoint:
Feel free to get back to me if you need any assistance.
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