go-ethereum/rpc 上公开的方法似乎不起作用

问：

我有以下工作代码，我可以使用 cURL 来验证 RMI 是否存在，但是当我尝试调用它时，它说它不存在。

我的最小可重现示例：

package main

import (
    "log"
    "net/http"

    "github.com/ethereum/go-ethereum/rpc"
)

type ExampleService struct{}

func (e *ExampleService) Add(a, b int) int {
    return a + b
}

func main() {
    // Create a new RPC server
    server := rpc.NewServer()

    // Register a function to be called via JSON-RPC
    server.RegisterName("example", new(ExampleService))

    // Start an HTTP server to listen for requests
    http.Handle("/", server)
    log.Fatal(http.ListenAndServe(":8545", nil))
}

如您所见，RMI 示例存在：

$ curl -X POST -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"rpc_modules","params":[],"id":1}' http://localhost:8545   

{"jsonrpc":"2.0","id":1,"result":{"example":"1.0","rpc":"1.0"}}

当我尝试调用它时，它失败了：

$ curl -X POST -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"example.Add","params":[3,4],"id":1}' http://localhost:8545

{"jsonrpc":"2.0","id":1,"error":{"code":-32601,"message":"the method example.Add does not exist/is not available"}}

我做错了什么？