SMS verification falining for the wrong cause

Manuel Alejandro Lazo Menendez, When the SMS vendor says your URL is not reachable, it means their system cannot make a plain HTTPS GET to your callback address even if you can load it in your browser. Any DNS lookup failure, connection timeout, TLS certificate problem, or HTTP status other than 200 will trigger that error.

• To fix this, first allow fully public HTTPS access to your endpoint. In your Azure App Service go to Networking < Access Restrictions and remove any rules so that all incoming traffic is accepted. Make sure the SSL certificate you’ve uploaded includes every intermediate certificate, not just the leaf.

Next, from a machine outside your network please run this.

curl -v https://your-domain.com/verification-endpoint

You should see a clean TCP connection, a successful TLS handshake with no certificate warnings, and a straight “200 OK.”

• Once you confirm that, give the exact same URL to the SMS team. Their verification should then pass. After that, you can safely re-enable your network or firewall rules but add a short-lived query token or an HMAC header that only their system knows. That keeps your endpoint locked down without breaking their reachability check.

If you still get “not reachable,” turn on detailed access logging in App Service (or use Kudu logs), note the timestamp, client IP and the exact HTTP status or TLS error you see, and share those log lines. That information will pinpoint whether it is timing out, being blocked, or failing certificate validation so we can zero in on the final fix.

Hope it helps!

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