How can I fix the authentication issue causing my app rejection?

Shopify Apps
1

  1. App must verify the authenticity of the request from Shopify.
    Expected HTTP 401 (Unauthorized), but got HTTP 404 from https://tictacsales.azurewebsites.net/api/webhooks. Your app’s HTTPS webhook endpoints must validate the HMAC digest of each request, and return an HTTP 401 (Unauthorized) response code when rejecting a request that has an invalid digest. Learn more about securing mandatory GDPR webhooks

    My app was rejected due to this reason. How can i solve it