As explained by Meta: “An exclusion-only custom audience is a type of customer list custom audience that can only be used to exclude people from your ad audience. Unlike a regular custom audience, an exclusion-only custom audience cannot be used to include people in your audience.” “As an advertiser, you can use a regular custom audience to include and exclude people from your ad audience,” Meta said. “If you use an exclusion-only custom audience, however, you can only exclude people from your ad audience. You can’t use an exclusion-only custom audience to include people in your ad audience, and you can’t change an exclusion-only custom audience to a regular custom audience after it’s been created.”