Loyalty Program for pos that uses customer display

[bombshellsweets]

We just opened a new physical location and we are trying to move over from Square to the Shopify POS.  We want to incorporate a loyalty program that is cheap (preferably free to start).  The biggest question I am looking for is what loyalty program use the customer display (we are using a second tablet for the customer display) as the interface for the customer to use the loyalty program