I’ve combed the internet looking for a solution and I have none.
For some reason, my page can’t add the facebook developer app. I don’t get the box that pops up asking to to allow even. When I click “go to app” it takes me back to my page. It IS verified, I’ve tried logging into the developer page and going from there and nothing works. I checked the “apps” section on my page and it says I haven’t authorized anything even.
You probably have always use HTTPS enabled on your profile, however in your app settings, you don’t have a valid HTTPS url listed.
Instead of logging in as the page, log in as a page admin (normal facebook user) and try adding the app.