Legal analysis: If Party A neither signs nor seals, the contract is invalid. If the parties conclude a contract in the form of a contract, the contract is established when both parties sign or seal it. Therefore, if Party A does not sign or seal the contract, the contract is invalid.

Legal basis: Article 490 of the "People's Republic of China and Civil Code" Where the parties conclude a contract in the form of a contract, the contract is established when both parties sign, seal or fingerprint. Before signing, sealing or fingerprinting, one party has performed its main obligations and the contract is established when the other party accepts it.

Laws, administrative regulations or the parties agree that a contract should be concluded in writing. If the parties do not do so in writing but one party has performed its main obligations and the other party accepts it, the contract is established.