http://www.businessinsider.com/what-is-facebook-audience-network-and-why-does-it-matter-2016-2
FAN (Facebook Audience Network) is not FCA (Facebook Custom Audience) which is what you have.
FAN is for mobile app publishers to earn money.
FCA is for businesses who want to advertise on Facebook website and App.
FAN made $1billion last year. But why do you refuse to add to your service?
Importato da support.iubenda.com (topic #42000003856) · 
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Hi, this is Simon, part of the iubenda core team. First, thanks for your tenacity regarding this topic. We understand that our users need us to be on the top of our game. So let me tell you about FAN:
As I’ve informed you before there are more elements that determine an integration like necessary translations, roadmap, or even fitness-for-purpose. Oftentimes we also encourage people to do their own integration since they just know the most about their own apps. Facebook Audience Network is no exception.
In the last 6 weeks we’ve added 37 new services to the generator and FAN is part of that latest push. It will be rolled out with the next newsletter, so stay tuned. We’re also going to inform in the forums in the relative posts, just to make sure no one misses anything.
Hope this helps. 
Simon