The data carried in the 1. request is encrypted or signed, but there are problems in server-side verification, such as failed signature verification or no signature.
2. The request lacks the necessary authentication or authorization information.
3. The client performed an unauthorized or illegal modification operation, resulting in the request being rejected. "Reverse engineering" can refer to reverse engineering or behavior contrary to normal operation. "POST" is an HTTP request method, which is used to send data to the server. "Illegal signature request" involves verification and authentication.