How to fix 403 error what Twilio calls my webhook?

Question

We're using Twilio. We have webhooks set up so that when Twilio receives a call, it forwards it to a URL on our site.

This appears to have been working fine. But now I made a change to the code, and suddenly Twilio is having problems calling the webhook. We don't receive the message, and if I look in the Twilio log, it says it got a 403 error. (I can't swear that this has never happened before. I've never noticed a message to be lost, but maybe I missed it while debugging other errors, attributed a lost message to something else.)

The truly strange part is, about 2/3 of the message that come in are received and processed fine, but about 1/3 get the 403 error. This is on a test server where we don't have any load balancing, so all requests are going to the same instance of our app. The tests I've been doing today are all from the same cell phone to the same Twilio number.

We do have authorization on the app, but the authorization is all on sub-directories, not the top level, and the sub-directory with our web hook has no authorization set up.

The first thing my our web hook now does when it gets called is send me an email with the content of the message from Twilio. (For debugging purposes.) I'm not getting that email, so I'm very confidant it's not getting called. And as I say, I can look at Twilio's log and it says that it received the text message and got a 403 error trying to forward it to my webhook.

The fact that it's only like 1/3 of the time is particularly puzzling. It's from the same number, to the same number, hitting exactly the same URL on the same site. Why would it work sometimes and not other times?

I tried to reproduce the problem on my desktop by calling the URL directly, not going through Twilio, and that does not give the same error. (It occurs to me as I type that the next logical test is to hit the page on the server without going through Twilio.)

Oh, the server is ASP.NET. The code is in VB but I doubt that matters as we're not getting as far as executing any of our code when it fails. When it doesn't get the 403, the code is working fine.

question from:https://stackoverflow.com/questions/65946401/how-to-fix-403-error-what-twilio-calls-my-webhook

Answer 1

Check your firewall configuration as it might block the requests.

If it does then whitelist requests originating from Twilio.

We're using AWS WAF and ran into a similar situation: We saw the requests erroring out with a 403 in the Twilio Debugger but the requests never hit our endpoints. Once we adjusted the whitelist the problem was gone.