I am having the same problem as described at Facebook App Center Listing for Website Platform.
However, I already entered my URL into "Site URL" on the "Settings" page and I reviewed https://developers.facebook.com/docs/games/appcenter/guidelines and I cannot see what I'm missing or doing wrong.
I have already integrated "Facebook Login" to my website and I would like to add it as a Facebook app. At https://developers.facebook.com/apps I added my app. On the "Settings" page, I filled in all of the fields under the "Basic" tab and I entered the same URL to both "Site URL" and "Mobile Site URL" on the "Website" platform. On the "App Details" page, I filled in all of the fields in the "App Info" section, except "Publisher". I filled in all of the fields in the "Contact Info" section, except "Marketing URL". I uploaded the two requested Icons. I uploaded all of the Web and Mobile banners, except "Large Web Editor's Pick". I uploaded 5 screenshots and the video.
Yet, in the "App Center Listed Platforms" section, the "YES/NO" switch for "Website - Mobile" is on "YES", but the "YES/NO" switch for "Website" is still greyed out with "NO" and when I hover over the ? mark, it shows this:
This platform cannot be listed because it is configured incorrectly or not supported in our App Center.
Can anyone provide any suggestions on how to get the "YES/NO" switch to work for "Website" platform?
UPDATE: user2284877 pointed out that Category has to be changed from "Game" to something else. This worked. So, is there no way to create a Facebook App for the "Website" platform and that is in the "Game" category?
Look at app details > category Change it from game(I presume) to fashion or something else :) worked for me.