Function protocol_error 

pub fn protocol_error(id: Option<&Value>, error: &RpcError) -> Value

JSON-RPC 2.0 reserves -32700 (parse error), -32600 (invalid request), and -32602 (invalid params) for requests that never reached application logic. Reporting those as -32001 “blocked by policy” (with HTTP 403) falsely told clients an authorization decision was made about a request that never parsed.