When changing the price of a product on the POS, you will be limited by the configured Price Change Range.
Eg. When the Price Change Range is 10%, and you have a $100 product, you will not be able to discount it to $80; the lowest you can make it is $90.
Change the Price Change Range
Go to Configuration > Company Profile > Basic Info
Enter the new Price Change Range for manager and staff
Sync modifiers on the iPad