I followed the directions on facebook to add my app (which is a tab) to my fanpage:
\"Facebook Page administrators can add your app directly to their
see the TUTORIAL here: https://stackoverflow.com/a/35287477/2377343
Go to your App Settings, then Basic and add a platform as page tab. Provide a URL with https, even if you don't have it, just to test. Then run this page and you can successfully add your app to the page tab.
Facebook has recently made changes to its developer interface and specially the App Dashboard. Hence it might be a bit tricky to find out how to configure the Page Tab. Refer the following tutorial - https://developers.facebook.com/docs/appsonfacebook/pagetabs/
If you want to add an app to your fanpage you need to fill in the "Page Tab" section With your site url
It sounds like your app isn't configured to actually provide a page tab - check the 'Page Tab' section of your app's settings to make sure you've configured it correctly.