Is it permissible to determine the price of a specific commodity in Tunisian Dinars before purchasing it from France, and how is its price paid in Tunisian Dinars after returning to Tunisia?

If you were an agent, a volunteer to purchase, and you bought the phone with a foreign currency before the principal gave you the money, then you are a lender to him, and it is not permissible to agree on repaying the loan with another currency (deferred exchange). However, it is permissible for you to ask him, upon your return, to repay in dinars at the exchange rate of the day of repayment without a prior agreement.

For the transaction to be permissible, there are two methods: 1. Murabaha sale to one who orders a purchase: This is limited to a promise that you will buy him a phone with specific characteristics and sell it to him at a known price in dinars. If you buy the phone and take possession of it, you then sell it to him according to the promise. 2. Salam contract: This is when you both agree on precise specifications for the phone, and you receive the full price in cash at the contract session, with the condition that the phone be delivered at a specific, known future date, based on the saying of the Prophet, peace and blessings be upon him: "Whoever pays in advance for something, let it be for a known measure and a known weight until a known time." If the price is not paid in full at the contract session, this contract is not valid.