Hello Steve,
Thank you for posting your question in the Microsoft Q&A Community.
I understand that you would like to know how to get your web app working again.
There are three reasons why you might encounter this error;
- The site has reached a billing limit and your site has been disabled.
- The Web app has been stopped in the portal.
- The Azure Web app has reached a resource quota limit that applies to either Free or Shared scale modes.
In your case, it is most likely related to the billing limit as you explained you adjusted your credit card expiration date.
Once your account is in good standing again, you can start the web app from the portal.
You can also take a look at this link which explains more about error 403 on Azure Web App.
If this issue persists afterward, I would advise you to raise a ticket to the Web App Team.
Let me know if further assistance is required.
Babafemi