The IOU or IOU only exists as evidence and is not a necessary condition for prosecution. The absence of IOU does not affect the parties to sue in the court. As long as the parties meet the prosecution conditions stipulated by the law, that is, the parties have an interest in the case, have a clear defendant, and have specific litigation claims, facts and reasons, they can sue even if there is no IOU. However, the parties may use other related evidence or indirect evidence, such as voice recordings with the debtor, bank transfer records, witness testimony, etc., as well as all evidence that can prove the fact of arrears and the amount of arrears, so as to clarify the existence of creditor debtor relationship between the parties. If the money is given in cash, the receipt for withdrawing cash from the bank should be printed.
 [Legal Basis]
 Article 119 of the Civil Procedure Law stipulates that a lawsuit must meet the following conditions:
 （1） The plaintiff is a citizen, legal person or other organization that has a direct interest in the case;
 （2） There are definite defendants;
 （3） There are specific claims, facts and reasons;
 （4） It falls within the scope of civil litigation accepted by the people's court and under the jurisdiction of the people's court to which the lawsuit is filed.