Audience Size Requirements
Facebook and Google have minimum audiences size requirements in order to serve ads to that audience:
Google Ads:
Google Search Network: at least 1,000 active visitors or users within the last 30 days.
Google Display Network: at least 100 active visitors or users within the last 30 days.
YouTube: at least 1,000 active visitors or users within the last 30 days.
Gmail: at least 100 active visitors or users within the last 30 days in the Display Network.
Facebook Ads audiences must contain at least 20 users.
LinkedIn Ads audiences must contain at least 300 members.