Attempting to push a custom audience results onto a Facebook Authorization Error visible in Notifications.
Some custom audiences can be pushed and it appears to be only affecting a certain Ad account.
1.) Check if the Custom Audience Terms (https://www.facebook.com/legal/terms/customaudienc) have been accepted
2.) Check in Audience manager logged in as the user used in the Facebook Custom Audience service in Marketo, to see if there are any custom audiences that have the "Accept Terms" button pop-up similar to this screenshot
3.) As per our recent release notes at https://docs.marketo.com/display/public/DOCS/Release+Notes%3A+Winter+%2719:
"Facebook now requires a Business Manager account in order to leverage your Custom Audience integration. Your Facebook LaunchPoint service must be associated with a Business Manager account or your integration will no longer work after January 14, 2019. To set up a Business Manager account, please refer to Facebook Help."
4.) Check if the user used in the Facebook Custom Audience service in Marketo is a Business Manager account
5.) After completing the checks above, try to push a custom audience again to the affected ad account. If unsuccessful, recreate the Facebook service and test to push a custom audience from there.