The item.adjudication [adjudicationamounttype] and adjudication [adjudicationamounttype] is 0..*.  The IG does not prevent a payer providing multiple slices with category = discount. There is a reason code on both adjudication and item.adjudication that the IG does not call out as Must Support.  However, there is nothing preventing a payer from using the reason code.  It is bound to an example value set that could be used to describe a reason for the discount.  Alternatively, if there are known discount types, the codesystem could be extended to enumerate them.