Is it permissible to take money from investors to pay for electronics purchased on credit, with an agreement on a profit percentage, and are they to be charged the same purchase price, and how are profits distributed, and what is the legitimate صيغة (formula/form) of a Mudarabah contract?

Mudarabah is not valid if the goods are already owned by you, as it is not permissible to buy from yourself or to engage in mudarabah with goods you already own.

You have several solutions:

1. If you cannot cancel the sale: Inform them that you own goods, and whoever wishes to participate with you in them can buy a share of them. You are the seller, and the other party is the buyer, and you must disclose that you are a seller making a profit, not an agent. This is mudarabah with commodities or a partnership with commodities, both of which are permissible. It requires valuing the goods to determine the capital and ascertain profit and loss.

2. Selling a specific quantity of goods with an agreement to sell them in the market: You sell a specific quantity of goods to your partner and agree with them to sell it in the market for a fixed fee for you, or a percentage of the goods or their profit. Upon sale, you give the price to its owner and take your fee or percentage.

3. Selling an undivided share of the goods: You sell an undivided share of the goods (such as a quarter or a percentage) after the buyer has inspected all the goods. The buyer becomes your partner in the specific goods, which is a "partnership of ownership." Agree with the partner to sell the goods for a fee or a percentage. When any part of the shared goods is sold, the price is divided among all according to their shares, and you take your fee or percentage.