2. If negotiation fails, you can entrust a lawyer to send a lawyer's letter to the developer. A lawyer's letter can play the role of reminding and warning the other party.
3. In the end, if the developer still refuses to solve the problem through negotiation and sending a letter, he can bring a lawsuit to the court, asking the developer to continue to perform the contract or demand the termination of the contract, and investigate the developer's liability for breach of contract.