Legal analysis: Only IOUs with official seals and no signatures of legal persons are valid. According to the laws of our country, an IOU that is only stamped with the official seal but does not have the signature of the legal representative is generally deemed to be valid. Unless the unit pleads that it only issued an IOU, but the counterparty did not fulfill the loan or deliver the goods, and the counterparty cannot provide evidence that it has fulfilled the obligation to the unit, the IOU may be deemed invalid.

Legal basis: Article 143 of the "People's Republic of China and Civil Code" is valid if the following conditions are met:

(1) The actor has the appropriate qualifications capacity for civil conduct;

(2) The expression of intention is true;

(3) It does not violate the mandatory provisions of laws and administrative regulations, and does not violate public order and good customs.