Facebook instant articles: can't enable the "submit for review" button, it's always greyed out

I'd like to configure facebook for instant articles with my website (http://ift.tt/1KPSnRj). I installed three plugins:

• Facebook Instant Articles & Google AMP Pages by PageFrog, in order to get the right styles for posts
• Instant Articles for WP by Automattic, in order to have the http://ift.tt/1VXWYJU feed
• WP-InstantArticles by Lester 'GaMerZ' Chan.

Actually just the second plugin would be enough but I then realized i needed something to style my posts according to instant articles specifications, so I installed Facebook Instant Articles & Google AMP Pages by PageFrog as well.

When i generated the feed http://ift.tt/1VXWYJU I noticed it does not contain at least 50 posts as facebook settings require: my website contains far more than 50 posts so I was wondering why was the feed limited to a smaller number; being Instant Articles for WP the official wordpress plugin for instant articles I expected it to generate a compliant feed.

In order to get a fuller feed I installed the third plugin and got another feed: http://ift.tt/1Npq7XL This one includes 50 posts but it doesn't work either. I tried pasting both feed URLs in the configuration page

expecting this to enable the "Submit for review" button, but it does not.

Did anybody experience similar issues? How did you solve it?

Thank you Marco

via Chebli Mohamed