Signup email confirmation onclick button stopped work with no code change?! Help appreciated

so I've encountered a problem where the submit button on a web page built on the Microsoft Azure platform is not responding as it should.

After entering their information and clicking submit the site should redirect to the thank you page and automatically send the user a confirmation email.

It was working fine before, and the code has not been changed since.

Anybody have any idea why would be super helpful thanks.

Maybe be helpful idk: The submit button has an onclick function call __doPostBack(...)

Thanks for the help.