Is it permissible to pay a sum of 1000 US dollars in Libyan dinars according to the exchange rate on the day of transfer, or must it be paid in dollars?

Transferring money via Western Union is considered an authorization for it to deliver the amount. If the transfer is in the same currency, it is a pure agency. If it is in a different currency, it is a currency exchange and an agency, and possession must be realized in it, even if it is constructive. As for a prior agreement to exchange different currencies, it is not permissible because it constitutes a deferred exchange. However, it is permissible at the time of payment at the rate of the payment day, with mutual possession.