Under the name of each item of the order, there is a link titled "Cross sales". Clicking the link opens up a window with two groups of items: "Purchased with this product" and "Analogues".
In the form that opens, you can, without leaving the order, browse the various product analogues in your warehouse, as well as additional products that are usually bought along with the selected item in the order.
These products can also be added to the order. For example, when talking to a customer, you can quickly replace a missing product with an analogue or carry out an up-sale by suggesting an item that is usually purchased with the current order-items. Related products are selected either according to the rules described in the "Product page" section, or according to a recommendation system, for example, RetailRocket.