The IOU is not invalid with my signature, but valid with my voluntary ratification. The following factors will also affect the validity of IOUs: 1. The date of the debt-be sure to write it clearly, preferably accurate to the day, and you can agree on the repayment date in the IOU. If the repayment date is not agreed, the creditor may claim to return it at any time. If the repayment date is agreed, it can only be required when the repayment date expires. 2. The amount owed should be capitalized in Arabic numerals and Chinese at the same time, and the currency should be clearly written. 3. If the debtor is married, it is better to obtain the signature of the spouse, which is more secure for the creditors, and avoids that one party refuses to undertake the repayment obligation or execute it in court on the grounds of ignorance, and one party transfers the property to the spouse, resulting in inability to repay. 4. A copy of the ID card and marriage certificate signed by the debtor shall be collected at the same time.