Issue
An audience that was created in Engage has not yet come up in the Facebook Custom Audiences Destination.
Product
Twilio Segment
Environment
Segment Console
Cause
A newly created audience can take about 10 minutes to show up in your Facebook Custom Audiences Destination, and even longer if it's an unusually large one.
Resolution
Wait at least 10 minutes, then check again. You can check by going to Business Manager > All tools > Assets > Audiences within Facebook Ads.
Additional Information
For additional details, please check out our documentation below: