When a Customer Facing Display is assigned to a POS station it is also necessary to set the receipt prompt for cash and credit card transactions within the Management console. This will allow the customer to choose if they want to print a receipt on the display unit. 

To make this change login to the Management console, click on 'Settings' then 'Receipts' and under 'print cash receipts' and 'print credit receipts' select 'Prompt'. Save the new setting. Logout from your POS stations and refresh them.