What are the limitations or restrictions when using custom audiences?

When using custom audiences in Facebook advertising, there are some limitations and restrictions to keep in mind. Here are some of the key limitations and restrictions:

1. Data source requirements: To create a custom audience, you need to have a data source that contains customer information, such as email addresses, phone numbers, or app user IDs. The data source must also meet Facebook's data collection and storage requirements, which include obtaining explicit consent from users to use their data for advertising purposes.
2. Audience size: Custom audiences must contain at least 100 people to be used for advertising. If your audience is too small, Facebook may not be able to target your ads effectively.
3. Data freshness: Custom audiences must be updated at least every 90 days to ensure that the data is still relevant and accurate. If your audience hasn't been updated within the past 90 days, Facebook may stop delivering your ads to that audience.
4. Ad targeting restrictions: There are some restrictions on how you can target ads to custom audiences. For example, you cannot use custom audiences to target people under the age of 18, and you cannot use custom audiences to target people who have opted out of receiving your ads.
5. Data privacy restrictions: Facebook has strict data privacy policies that must be followed when using custom audiences. For example, you cannot use custom audiences to target people based on sensitive information, such as their race, religion, or health status. You must also ensure that you have obtained explicit consent from users to use their data for advertising purposes.
6. Lookalike audience restrictions: When creating lookalike audiences based on custom audiences, there are some restrictions on the audience size and location. For example, lookalike audiences must contain at least 1,000 people in the source country, and you can only create lookalike audiences for countries where Facebook has sufficient data to create accurate audiences.

Overall, custom audiences can be a powerful tool for targeting ads to specific groups of people, but it's important to follow Facebook's limitations and restrictions to ensure that your ads are effective and compliant with data privacy regulations.