The View by Items option in the Promotion Detail report is not available for check-level promotions as these promotions apply to an entire check and not individual items. Only item-level promotions are applied to specific menu items on a check, so only these types of promotions have a View By Item capability. Refer to your POS setup to adjust whether your promotions live at the check-level or item-level.
Item-level discounts should be used when tracking situations such as customer dislike, service issues, and/or long waits. On the other hand, a check-level discount is applied to the overall bill, regardless of what items were ordered, like a local's discount or loyalty program discount. This type of discount can be useful for restaurants that want to offer a promotion or discount to their customers as a whole, without focusing on any specific menu item.