To limit the amount of discount the Staff can apply, you can set the Limit in your Indica Account under Config, then in Settings.
Once on this page, scroll down until you see Discount Limit. There you can enter the percentage amount that will be the maximum any Staff can enter up to. It will prompt a Mangers Pin for any discounts above this setting for regular Staff.
Make sure to click on SAVE for these settings to take effect.
Now any transactions with Discounts applied over the limit will be restricted and will require a Manager to enter their PIN to override it.