Why can I access the billing portal?

The billing portal is available to users with our Full Access permission set. If you have the permission set assigned to your user, you may be using a Salesforce Classic tab in Lightning. Classic used iframes, which are no longer supported. When you try to open the portal, it will be a blank page with the stripe logo.

"Emma Settings" is the Lightning tab. Emma Settings (Admin) is the Classic tab. You can edit the tabs of your existing app or change to using our Lightning app. Apps are managed in Setup>Manage Apps.