These are the main reasons why you may experience this issue:
- You created your Ad Account recently.
- You have been using your Ad Account for a long time now but you have a newly created Business Manager.
- Both your Ad Account and the Business Manager are not new, but you associated your Ad Account with the Business Manager recently.
For now, you should wait for a couple of weeks and do not violate Facebook Advertising policies.
Please share your custom audiences with another Ad Account that is also associated with the Business Manager or wait until your current Ad Account is eligible to accept the audiences.
We'll notify you by email when your Ad Account becomes eligible to accept shared custom audiences.