Dear Mr. Robert, Although we sent you your goods on time, we have waited nearly two months for you to pay the balance of $ 5000, which is over due. When you ordered the shipment of computers, you requested that we send you the entire order no later than June 1 , and we shipped the goods by air freight on May 25. As you agreed in our original credit arrangement (赊账协议) , payment was due in 30 days, on June 30. Yet, as it is already August 26, we still have not received your payment. In fact, we have not received any answer to the notice we sent to remind you that the payment was due. We regret to say that if we cannot receive your payment by September 15 , we will be forced to ask our lawyer to take measures and collect it through legal procedures. Yours faithfully, Adam Smith The Western Company What's the purpose of the letter? To urge the buyer to______.