If you don't see all of your Facebook Custom Audiences on the list when prompted to select one to sync in Klaviyo, you might be using an unsupported audience subtype (which won’t show up on the list). 

There are different Custom Audience data sources that Facebook accepts. 

Klaviyo only supports the following subtypes when syncing with Facebook: 

• HASHES: Email hashes or phone hashes
• HASHES_OR_USER_IDS: Email/phone hashes or user ids
• MULTI_HASHES: Created from multiple types of hashes at the same time
• COPY_PASTE_EMAIL_HASHES: Emails entered manually via Facebook's Ads Manager
• DATA_FILE: Data files

Since we aren't able to sync with other audience subtypes, we won't show them on the list of available audiences when you attempt to sync a list or segment in Klaviyo.