A person bought merchandise from another. They agreed that the buyer should pay for the goods in three…

A person bought merchandise from another. They agreed that the buyer should pay for the goods in three months’ time. However, the buyer could not pay the debt on time. Both the parties agreed that the debtor should be given another three months to come up with the money provided that an additional amount is paid on top of the original debt. Is this transaction shar‘ī?