Payments2Us Vouchers provides the ability to provide a Voucher to Customers/Members/Event Attendees.  Vouchers are also known as Promo Codes, Discount Codes or Coupons.

In Payments2Us you setup a Voucher Type.  This is a template for the Vouchers that are subsequently created.

Once a Voucher Type has been created, you then create related Vouchers by manually creating them in Salesforce, or you could use Process Builder to create Vouchers.

Your provide your members/customers/event attendees with a voucher code.  On the checkout form, they enter the voucher code to get apply the voucher discount (percent / amount)