Legal analysis: If the contract is written and only signed by Party B, but not signed and sealed by Party A, the contract is invalid. If the contract is electronic, a confirmation letter must be signed in advance, otherwise the contract will be invalid. Since it is a contract, it needs to be signed by both parties.

Legal basis: Article 464 of the Civil Code of People's Republic of China (PRC). A contract is an agreement between civil subjects to establish, change and terminate a civil legal relationship. Agreements on status relations such as marriage, adoption and guardianship shall be governed by legal provisions on such status relations; If there are no provisions, the provisions of this part can be applied according to their nature.