Suggested readings: Architect Channel Facebook Custom Audiences, Using Facebook Custom Audiences
Does Facebook Custom Audience need a long time to populate?
It depends on the number of users in the journey and their activity. For example, if the website has 1 million users per day, it will take a short time to populate. Also, the Facebook element works in real time to populate selected custom audiences.
Can I send users’ attributes or events to the custom audience?
Facebook does not allow this for privacy reasons. Nevertheless, you can segment users in the Check Conditions and Starter elements to determine which segments are passed to custom audiences.
How do I know if users have been matched after they’ve been passed to Facebook?
Facebook does not provide this information for privacy reasons.