HTTP Error 403.60 - Forbidden When posting form on azure web app

I'm in the process of moving an on premise app to azure web app. When i try to submit a form using post on any action, the application returns an iis error message of HTTP Error 403.60 - Forbidden. All the get requests are working correctly, this issue doesn't occur when running the application on a local IIS.

Can anyone suggest what to check? I have other azure web applications that submit posts and dont have this issue.