Various suppliers offer purchase discount and are recorded in the Manager. Is there a way to extract the total discount offered on each of the invoices by suppliers for a particular period?
Not really. The trouble is that discounts can be specified as percentages or exact amounts. Neither variable is exposed for custom reports. (They are different variables, as can be seen when doing Batch Update operations.) And, although either percentage or exact amount will be stored in the database, the amount of discount applied on a line item is not passed to a transaction form for display. Instead, the
Amount field is calculated using whichever is populated. In other words, the arithmetic is invisible to the user and, in the case of a percentage discount, the reduction is not stored at all.
One way around this is to enter all discounts as separate line items, describing them with standard terminology. Then, you could create a custom report with appropriate filtering to find those transactions. See https://www.manager.io/guides/24843.