@Lito Juliano Thanks for reaching here! There are three conditions can cause this error:
- The web app has reached a billing limit and your site has been disabled.
- The web app has been stopped in the portal.
- The web app has reached a resource quota limit that might apply to a Free or Shared scale service plan.
To see what is causing the error and to resolve the issue, follow the steps in Web Apps: "Error 403 – This web app is stopped".
Hope this helps, please let us know if issue remains.