What is the ruling on an agent purchasing an item with a currency different from the currency given to him by the principal?

If the agent deviates from his principal's instructions regarding the currency of the price, and purchases with a currency other than the one specified by the principal, then his action is subject to the rule of the fuduli (unauthorized agent). If the principal ratifies it, the purchase becomes binding upon him; otherwise, it becomes binding upon the agent. If the principal ratifies the purchase, the goods belong to him, and he owes the equivalent of the dollars paid. If he does not ratify it, the goods belong to the agent. If the dollars are established as a debt owed by the principal, and the agent agrees to be paid in another currency, this is permissible, provided that the payment is made at the market rate of that day and that they do not separate while anything from the exchanged amount remains outstanding between them.