'Authorization Required' error on Lightning Platform sites

Troubleshooting Managed Package License Issues

If your Force.com site uses managed packages, the site's guest user may need a managed package license. To check and assign managed package licenses to the site guest user:

1. Ensure you have the "Manage Users" and "Manage Package Licenses" permissions.
2. Go to Setup > Develop > Sites > select your site.
3. Click the "Public Access Settings" button.
4. Click the "View Users" button.
5. Click on the Sites Guest User to open the user detail page.
6. Scroll down to the Managed Packages section.
7. Click the "Assign Licenses" button and assign the license for each managed package used by the site.

Troubleshooting Visualforce Page Errors

If the error is caused by a Visualforce page error, use the following steps:

1. Enable debug logs for the site's guest user and attempt to access the page to capture the debug log. Review the log for errors.
2. If debug logs do not provide enough information, use the Preview as Admin feature. Return to the site detail page (Setup > Develop > Sites > select your site) and click "Preview as Admin" with developer mode enabled on your user record. When the Authorization Required page loads, it displays the type of error at the bottom of the page if it is caused by a Visualforce page error.

The Preview as Admin feature allows administrators to view Force.com site pages as an admin user to diagnose errors that the guest user cannot describe. It is available on the site detail page in Setup.