There is no IOU. If the debt relationship between the two parties can be proved by other means, the debt can also be recovered. Such as audio and video recordings, transfer records, etc.
[Legal Basis]
According to Article 63 of the Civil Procedure Law, evidence includes:
（1） Statement of the parties;
（2） Documentary evidence;
（3） Physical evidence;
（4） Audio-visual materials;
（5） Electronic data;
（6） Witness testimony;
（7） Expert opinions;
（8） Record of inspection.
Evidence must be verified before it can be used as the basis for ascertaining facts.
