Facebook Ads gets rejected – Web Applications Stack Exchange

I have a web shop, for sports wear. I have fb page as well. But, whenever I try to advertise, for example, grid photo of few shoes, and recently just a link to a web site (web shop in shopify), I get following error:

Error message from Facebook: This ad isn’t running because it promotes content that is against Advertising Policies.Our policies are in place to keep users safe and foster a positive global community. (https://www.facebook.com/policies/ads)

Does anyone have a clue what can be a problem?

I read those policies, and found nothing wrong.