Is a sale conducted in Iraqi Dinars in exchange for Saudi Riyals, where the exchange was not made in the same sitting, but rather the payment was made three days later, Islamically permissible? And what is the solution to rectify this contract? And is it permissible to re-contract with immediate exchange?

Exchanging currencies with one another is considered sarf (money exchange), and it is only valid if it is done hand-to-hand, meaning that one currency is handed over and the equivalent of the other currency is received immediately in the same session of the contract without delay. The proof for this is the saying of the Prophet, peace and blessings be upon him: "If it is hand-to-hand, then there is no harm; but if it involves delay, then it is not valid."