If you wish to recover the debt without taking your business partner to court dispute, DEMAND LETTER will be a appropriate answer.
The purpose of DEMAND LETTER is to secure concrete evidence to prove that creditor has demanded for repayment against debtor in public transcript form.
If you send a DEMAND LETTER to debtor, the post office will make 3 copies of letter, send one to debtor, return one to creditor, and keep one at the post office. The creditor can track the delivery status afterwards, of course.
DEMAND LETTER can be a powerful evidence since the government (post office) keeps one of the original copies and the creditor can check if debtor has received the letter, which means, the debtor has been asked to pay for the unpaid balance.
By sending DEMAND LETTER, creditor can also stop the progress of statute of prescription. However, creditor should file a lawsuit within a certain period, in Korean Law, 6 months.