Keep in mind that even though all Custom Audiences show up, only those in "Ready" serving status will properly target users in your campaign.
For List Custom Audiences, we recommend expanding the reach during campaign setup. This feature finds people on Twitter who are similar to the people on your List Custom Audience, and targets them in your campaign as well.
This is a great way to maximize your campaign's ability to serve if your List Custom Audience matches a relatively small number of users, and to drive more volume in your campaign. Reach expansion is optional, and can be toggled on and off in your campaign.
You can also choose to "Add" or "Exclude" the users in your Custom Audiences:
- Add: The users in your Custom Audience will be served the Tweets in your campaign, if they meet the geo, gender, age, and device targeting criteria specified in your campaign.
- Exclude: The users in your Custom Audience will NOT be served the Tweets in your campaign, even if they meet the other criteria in your campaign.
To respect user privacy, the minimum size for a Custom Audience to be usable is 100 Twitter users. If your List Custom Audience is under 100 Twitter users, it will display as "Audience too small" and will not be available for targeting.