Why am I getting an error message saying that the audience is too small on our Facebook Ad?

If you’re getting an error message saying that the audience is too small on your Facebook Ad, that error message means that you have fewer than 20 people in your Facebook Ads list. Facebook requires you to sync at least 20 people per list in order to advertise. If the list contains fewer than 20 people, Facebook will not allow you to advertise to a custom audience. If an email address is not found then the customer will not sync from Klaviyo to the Facebook list.