What is the ruling on working with the Makazin platform, which allows a user to display their products in their own store (for example, on the Salla platform), and then, when a customer places an order, the user pays the wholesale price of the product to Makazin, which then undertakes to ship it directly to the customer, knowing that the user does not purchase the product until after the customer's order?

There is no objection to displaying goods on platforms and selling them, provided that you own and possess the item before selling it. This is because the Prophet, peace and blessings be upon him, forbade a person from selling what he does not own, and from selling an item before possessing it. An exception to this is bay' al-salam (forward selling), which is the sale of a described item that is a liability, for an upfront price. So, if the customer pays the full price and the item is described, and a delivery deadline is specified, then it is permissible for you to purchase the item and request it to be sent directly to the customer. The buyer refers back to the seller (you) in case of a defect or an unfair deal.