server_fn stand alone with axum and reqwest

[maun]

Hi, I want to use server_fn without leptos, just with axum and reqwest.

I tried to piece something together but am stuck.
When running this as a client i get a "Request("builder error")", and for the server I do not know how to use the handler.
Has anyone tried this, or is there an example?

use server_fn::ServerFnError;
use server_fn::client::reqwest::ReqwestClient;
use server_fn_macro_default::server;

#[tokio::main]
async fn main() {
    #[cfg(feature = "client")]
    main_client().await;

    #[cfg(feature = "server")]
    main_server().await;
}

#[cfg(feature = "client")]
async fn main_client() {
    server_fn::client::set_server_url("127.0.0.1:8080");

    // prints Err(Request("builder error"))
    println!("{:?}", hello_world().await);
}

#[cfg(feature = "server")]
async fn main_server() {
    let router = axum::Router::new().into_make_service();
    // TODO: attach handler for hello_world
    
    let listener = tokio::net::TcpListener::bind("127.0.0.1:8080")
        .await
        .unwrap();
    axum::serve(listener, router).await.unwrap();
}

#[server(client = ReqwestClient)]
async fn hello_world() -> Result<String, ServerFnError> {
    println!("I am the server");
    "Hello, world!".to_string()
}