What is the legal ruling on selling electronic devices at retail, when the goods are not in the seller's possession at the time of agreement, but rather are purchased from the supplier after the customer pays a portion of the amount, and does this fall under the prohibition of "Do not sell what you do not possess"?

If the agreement is for the manufacturing of devices or the establishment of an electronic network, it is an Istisna' (manufacturing) contract, which is permissible, and it is not required to pay the full price at the time of the contract.

If there is no Istisna' and it is the sale of devices you do not own, it is not permissible except through the form of a Salam (forward sale) contract, which requires the full price to be paid at the contracting session.

Other alternatives include Murabaha and Wakala bi Ajr (agency for a fee). In Murabaha, the customer is promised that the device will be purchased, and after its ownership and possession are acquired, it can be sold in installments or for a spot price. In Wakala bi Ajr, the device is purchased for the client in exchange for a percentage or a fixed fee.