The contract is invalid, and a one-time contract needs to be signed or sealed by both parties. It is suggested to negotiate salary, but it is difficult to get salary if you don't do it for a month. First of all, you have broken your original promise to work for a month, regardless of whether the contract is legal or not.

According to the Contract Law of People's Republic of China (PRC):

Article 32

If the parties conclude a contract in the form of a contract, the contract shall be established when both parties sign or seal it.

Article 44 A legally established contract shall come into force upon its establishment.

Where laws and administrative regulations stipulate that examination and approval, registration and other procedures shall be handled, such provisions shall prevail.

Extended data:

Legal characteristics of contract

1. The contract is a legal act of both parties. That is, two or more parties need to express their will to each other (meaning expression is an act of expressing their will that can produce civil legal effect).

Both parties must reach an agreement on the expression of will, that is, the expression of will should be consistent.

3. The contract aims at the occurrence, alteration and termination of civil legal relationship.

4. A contract is an agreement reached by the parties under the condition of meeting the requirements of legal norms, so it should be a legal act.

Once the contract is concluded, it has legal effect immediately, and there is a relationship of rights and obligations between the two parties; Or change or eliminate the original civil legal relationship. If one or both parties fail to perform their obligations under the contract, they will be liable for breach of contract according to the contract or the law.

Reference: Baidu Encyclopedia-People's Republic of China (PRC) and China Contract Law