You can negotiate with the other party to ask the other party to issue a debit note or receipt. If the other party refuses to issue it, it can collect bank transfer records, call recordings, content of SMS exchanges, witness testimony and other evidence that can prove the fact that the repayment has been made to prevent the other party from suing against the IOU.
 [Legal Basis]
 In Article 2 of the Provisions on Several Issues Concerning the Application of Law in the Trial of Private Lending Cases, when a lender brings a private lending lawsuit to the people's court, it shall provide evidence of creditor's rights such as IOUs, receipts, IOUs, and other evidence that can prove the existence of the legal relationship between lending and borrowing.
 The people's court shall accept a civil loan lawsuit filed by the party holding the creditor's right certificate if the creditor's right certificate, such as the receipt, receipt and IOU, does not specify the creditor. If the defendant raises a factual defense against the plaintiff's creditor qualification, and the people's court considers that the plaintiff does not have the creditor qualification after examination, it shall rule to dismiss the lawsuit.