Legal analysis: A supplementary contract has legal effect only if it meets the following conditions: the parties to the contract have corresponding capacity for civil rights and capacity for civil conduct, but the subject does not, and the contract cannot have legal effect. The expression of will of the parties to a contract means that the expression of will of the actor should truly reflect his inner meaning. After the contract is established, it is often difficult to judge whether the parties' expression of will is true from the outside, and the law generally does not take the initiative to intervene. Even if the will is not true, the lack of the element of true will cannot completely invalidate the contract.

Legal basis: Civil Code of People's Republic of China (PRC).

Article 144 A civil juristic act performed by a person without capacity for civil conduct is invalid.

Article 146 A civil juristic act by the actor and the counterpart with false intention is invalid. The validity of a concealed civil juristic act with false intention shall be handled in accordance with relevant laws and regulations.

Article 153 A civil juristic act that violates the mandatory provisions of laws and administrative regulations is invalid. However, unless mandatory provisions do not invalidate civil legal acts. A civil legal act that violates public order and good customs is invalid.

Article 154 A civil legal act in which the actor colludes with the counterpart in bad faith and damages the legitimate rights and interests of others is invalid.

Article 505 The validity of a contract concluded by the parties beyond the scope of business shall be determined in accordance with Section 3 of Chapter VI of Part I of this Law and the relevant provisions of this Chapter, and the contract shall not be deemed invalid because it exceeds the scope of business.