The number of people in my Facebook custom audience does not match the number of people in my Klaviyo list. Why is that?
When you sync a Klaviyo list or segment to a Facebook Custom Audience, a percentage of the email addresses you attempt to sync may not match with an existing Facebook account. Because of this, your Facebook Custom Audience size may be smaller than the linked list or segment in Klaviyo. Facebook will not return an error, but won’t add any contacts who have email addresses that don’t match to an existing Facebook account.