The Zenoti system allows multiple discounts to be applied for each line item (invoice item id) within an invoice. The total discount for an invoice item id is captured in the 'Sales' data source, but it is NOT split out by the various campaigns applied. This data source goes a step further and breaks out the discount by campaign for each invoice item id. It ONLY brings in invoice item ids where a discount has been applied (through a campaign, coupon, or voucher). Other invoice item ids are NOT brought in. Additionally, manual discounts are NOT brought in to this data source.
Total discount by campaign
Total discount in a given time period (apart from manual discounts)