It's not illegal. It turns out that this IOU exists. If the other party does not question the fact of the loan, the court will naturally make a judgment. It is invalid for the creditor to tamper with the loan date without authorization, and it is impossible to verify the authenticity of the loan if the loan date is modified without authorization. The IOU is modified, the legitimacy of IOU is destroyed, and the effectiveness of IOU needs to be proved again. If the other party's tampering is proved and there is evidence to prove his point of view, the court will think that the other party's IOU is forged and will not recognize the creditor's rights relationship. (1) Numbers should be uppercase and lowercase.

When writing IOUs, check whether the decimal point position is accurate. There should be no spaces in front of the numbers, and the case does not match, otherwise the holder will add or modify the numbers, causing unnecessary disputes.

(2) Don't write with faded ink.

It is not advisable to write IOUs with ballpoint pens or other faded ink. If you write this way, the handwriting will become blurred after improper preservation, dampness or flooding, and it will also leave an opportunity for people with ulterior motives to alter it with chemicals and create troubles.

(3) The content should be clearly expressed.

Some IOUs say "buy" means "sell", "receive" means "pay" and "borrow" means "borrow". These are very easy to be reversed and it is difficult to distinguish right from wrong. A word difference, the result is very different.

(4) The name information should be complete.

IOUs have anonymous surnames or anonymous surnames, so the holders of IOUs should pay special attention, because this may leave the possibility and opportunity for the IOUs writer to breach the contract. In addition, ID card information is also essential.

(5) seals should be standardized.

Generally, I have to sign the IOUs and press my handprint. If someone else writes or signs on behalf of you, just press a handprint on the loan slip, it is easy to have disputes, and it will be difficult to identify the responsibility then. Only the debt written by the debtor will have judicial effect. No matter whether the date has been tampered with by others or other information in the debt, it can no longer make the debt continue to have judicial effect. However, if the debtor can't provide exact evidence to prove that the creditor did change the relevant information of the IOU, then the rights and interests may not be guaranteed.

IOUs should be written according to the format of our country, with detailed information such as name, loan time, loan amount and loan interest. If both parties borrow successfully, they shall repay the arrears within the time specified in the loan. Refuses to pay, should bring a lawsuit to the local people's court.