The Add to Custom Audience workflow action adds a contact to a particular custom audience on Facebook. Use it to retarget contacts with your products or services if they haven't yet converted as a lead, or to re-engage them after a purchase.
To get started, click the + icon to add a new workflow action and select Facebook - Add to Custom Audience.
Next, choose the appropriate Facebook Account ID from the dropdown menu.
Once the Facebook Account ID has been selected, choose the Facebook Customer Audience ID from the dropdown, which is where the contacts will be added.
After selecting the Audience ID, save your action to set it in the workflow and finish your setup as normal.