Meta (formerly Facebook) has supported and recommended ‘Value-Based Customer Lists’ since 2017. It has been best practice for advertisers ever since, yet Klaviyo still does not support them. Where this was once a ‘new feature’ that Klaviyo doesn’t support - it has gradually matured into being a glaring omission of the Klaviyo x Meta integration.
Put simply, this feature enables audience uploads to feature a ‘Lifetime Value’ column for each customer - so that Meta can create lookalikes weighted towards your most loyal/valuable customers; rather than finding lookalikes of low-value customers, which results in you finding more prospective low-value customers.
Klaviyo has data available to support the ‘value’ column in their Meta audience uploads, but this feature requires their attention and some prioritisation in order to deliver the baseline feature support that empowers the Custom Audiences they create.
Here is some additional documentation: https://www.facebook.com/business/help/1033094474356222
And a screenshot with a top-line explanation of the feature: