The Add to Custom Audience workflow action adds a contact to a particular custom audience on Facebook. This workflow action allows you to add contacts to a custom audience to retarget them with your products/services if you have not yet gained them as a lead, or want to retarget them after a purchase.
Firstly, click on the designated + 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, the user can then choose the Facebook Customer Audience ID from the dropdown menu, where they want the contacts to be added.
After selecting the Audience ID save your action to set it in the workflow and finish your set-up as normal.