You can go to the court to file a lawsuit if you are cheated of writing the IOU, claiming that the IOU is invalid. The court will review the "IOUs" with defects in form, and it is better for individuals to provide relevant evidence, determine whether there is a lending relationship in combination with other evidence, and loan cash delivery;
 It can comprehensively judge whether there is a legal and true relationship between the two parties according to such factors as the delivery of vouchers, payment capacity, trading habits, the size of the loan amount, the relationship between the parties and the transaction details stated by the parties.
 [Legal Basis]
 In Article 143 of the Civil Code, civil juristic acts that meet the following conditions are valid:
 （1） The actor has corresponding civil capacity;
 （2） True declaration of intention;
 （3） It does not violate the mandatory provisions of laws and administrative regulations, and does not violate public order and good customs.