If, for example, B pays A to make something by a certain date and A agrees but fails to finish by the specified date due to unforeseen extra costs but then A says if you pay me a little more I will finish by the date you wanted and B agrees, would this be known as a counteroffer? So now there is a different contract and A cannot simply pay the initial amount as he'd be breaching the terms of the new contract? I'm not too sure if this would be known as a counteroffer or not and can't find much on the matter. Thank you