You may have noticed that FB stopped allowing the upload of UID's when creating your ultra-targeted ads.
But don't worry...
FBLeadChef and FbGraphBeast both work perfectly well... and you can still create your Custom Audiences.
You can still upload "@facebook.com" Emails into Facebook's Custom Audience Editor.
So, instead of saving the UID's, save the Emails instead.
Then, choose the "Email" option in Facebook's Ad Manager.
And you should be good to go :)
Hope this helps!