You can add a product to a customer's order using Shopify Flow using your own custom logic. For example, you can add a product to a customer's order as a free gift for being a loyal customer if they match certain conditions on an order.

Shopify Plus customers may find this node useful when adding preorder, loyalty bonuses, or other products to a customers order without having to individually update each order individually. For example, you can tag orders a certain keyword such as "add-fee" and then add a digital product to a customer's order that can be invoiced to their account.

OrderEditing supports dynamically adding and removing products from a customer's existing order inside of Shopify Flow.