Hello HostingRising,
Navigate to the
Promotions module in BILLmanager --> Add a new Promotion, and set up its Conditions.
You can create discounts for all your customers in that module as well. If you create a discount in Clients --> Discounts, it will be assigned only to a certain customer.
I hope this article will help you
Discounts and Promotions in BILLmanager