Installation document for Discount at Checkout: offer Percentage or Fixed
Change Status into Enable and edit another settings as image 4.
Go to Catalog ➔ Information ➔ Write some explain for your discount and get friendly SEO URL to fill in Discount Detail Page.
2. Add permission
Login to your Opencart admin and go to System ➔ Users ➔ User Group.
Click edit your user group name (Opencart default user group name is Administrator as Image 2.1).
Check both Access permission, Modify permission for Discount Pack as image 2.2.
Go to Extensions ➔ Modules ➔ Click install Discount Pack as image 3.
Unzip downloaded package and choose exact folder for your Opencart version.
Then you will see the file Discount Pack OC v*.* - v*.*.ocmod.zip or only ***.ocmod.xml.
Go to your Opencart admin panel ➔ Extensions ➔ Extension installer.
Upload file ***.ocmod.zip or ***.ocmod.xml ➔ Continue as image 1.1.
Go to Modifications ➔ Click clear ➔ refresh buttons as image 1.2. This will remove and regenerate new cache for extension.