Why is the quantity discount applied even though the item is split across multiple lines?

When the same product appears on more than one line within the same invoice or order, the system aggregates the quantities of these lines together (for the same product and unit), and evaluates the quantity discount eligibility based on the aggregated total quantity, rather than each line’s quantity individually.

For example: if the minimum threshold to apply the discount is 10 units, and the product was purchased across two lines with 5 units each, the system considers the total to be 10 units, and automatically applies the matching tier price to both lines — ensuring the customer gets the correct price regardless of how the quantity is distributed across the lines.

Note: if the aggregated total quantity later drops below the required threshold (by deleting a line or reducing a quantity), the system automatically reverts to the next matching lower price tier or the base price.