Is it permissible to conduct a sale in which the seller and buyer agree upon a spot price for the commodity, and the price increases by a certain percentage (10% or 20%) if the payment of the price is deferred for more than three months?

If the seller and buyer agree on a specific price for the goods for immediate payment, and a higher price by a certain percentage if payment is delayed for more than three months, and the transaction on which the sale will be concluded is specified before they part ways, then this is permissible. However, if they part ways without specifying which of the two transactions will take place, then this is not permissible because it falls under the prohibition of two sales in one sale.