Note: This feature is currently only available on iOS.
On the main page of the Tappr App add a custom price or if you've created items in the product library, select the appropriate item.
Tap on the quantity icon on the top right hand side of the price (pictured below).
From there tap on the three circles on the top right of the app (pictured below).
Select your preferred discount (pictured below).
For more information on how to apply a discount via the Tappr App, please watch the below video.