Here are common troubleshooting steps to make sure the Ads Manager account is displaying in the dropdown menu on the publish screen:
Confirm You Are A Full Administrative User
Ensure that you have full administrative privileges in both the Meta Business Manager and Ads Manager account.
Go to business.facebook.com and click on "settings"
Click on "People" under the "User" tab. Make sure your user account has "full control"
Click on "Ad Accounts" under the "Accounts" tab. Make sure your user account has "full control"
Confirm You Have Accepted Custom Audiences Terms & Conditions
Meta custom audience T&Cs must be accepted by every user looking to publish to an Ads Manager account:
Copy and paste the below URL into notepad or other text editor application: https://www.facebook.com/ads/manage/customaudiences/tos/?act={ENTERACCOUNTID}
Replace {ENTERACCOUNTID} with your ad account id (removing the brackets) and enter the edited URL into a web browser. Follow the on-screen prompts to accept the terms.
Confirm Meta Data Sharing Settings
Navigate to the publish screen and click "Connect to Facebook." If you are already connected, click "Disconnect" and then "Connect to Facebook."
In the data sharing popup, click "Edit Previous Settings"
Click "Opt in to all current and future businesses" and "Reconnect"
Now, you should be able to see the new Meta Ads Manager account in the publish drop down menu.
Still experiencing issues? Contact your Customer Success Manager for additional assistance.