Please add Two Field for Coupon. One is our own coupon which we are giving to our customer on total sale and in other Coupon which reimbursed. In first type of Coupon field coupon amount have to divided within all items and not will be deducted from net amount.It will be treated like discount. And In another field Coupon will not be divided. So we require 2 types of field Like A and B for coupon
Please check the attachment for your reference.