Can someone help me understand why my json extarctor not working here

[Irvingouj]

Summary

pub(crate) fn router() -> axum::Router<crate::RuimContext> {
    Router::new()
        .route("/add", post(add_friend))
        .route("/remove", axum::routing::post(remove_friend))
}

#[derive(Deserialize)]
pub struct AddFriendRequest {
    pub friend_id: Uuid,
}

#[derive(Serialize)]
pub struct AddFriendResponse {
    pub application_id: i32,
    pub friend_id: Uuid,
}

pub async fn add_friend(
    UserTokenExtractor { user_id }: UserTokenExtractor,
    Json(AddFriendRequest { friend_id }): Json<AddFriendRequest>,
    State(db): State<crate::db::Database>,
) -> Result<impl IntoResponse, ApiError> {
    let application_id = db
        .create_friend_application(user_id, friend_id)
        .await
        .inspect_err(|e| tracing::error!("Failed to create friend application: {:?}", e))
        .map_err(|_| ApiError::msg("Failed to create friend application"))?;

    Ok(Json(AddFriendResponse {
        application_id,
        friend_id,
    }))
}

and I get compile error like this

error[E0277]: the trait bound `fn(UserTokenExtractor, axum::Json<AddFriendRequest>, axum::extract::State<db::Database>) -> impl std::future::Future<Output = Result<impl IntoResponse, ApiError>> {add_friend}: Handler<_, _>` is not satisfied
   --> ruim-server/src/handler/user/friendship.rs:15:29
    |
15  |         .route("/add", post(add_friend))
    |                        ---- ^^^^^^^^^^ the trait `Handler<_, _>` is not implemented for fn item `fn(UserTokenExtractor, Json<AddFriendRequest>, State<Database>) -> impl Future<Output = ...> {add_friend}`
    |                        |
    |                        required by a bound introduced by this call
    |
    = help: the following other types implement trait `Handler<T, S>`:
              <axum::handler::Layered<L, H, T, S> as Handler<T, S>>
              <MethodRouter<S> as Handler<(), S>>
note: required by a bound in `post`
   --> /home/irving/.cargo/registry/src/index.crates.io-6f17d22bba15001f/axum-0.7.4/src/routing/method_routing.rs:389:1
    |
389 | top_level_handler_fn!(post, POST);
    | ^^^^^^^^^^^^^^^^^^^^^^----^^^^^^^
    | |                     |
    | |                     required by a bound in this function
    | required by this bound in `post`
    = note: this error originates in the macro `top_level_handler_fn` (in Nightly builds, run with -Z macro-backtrace for more info)

if I comment out this line Json(AddFriendRequest { friend_id }): Json<AddFriendRequest>, then everything compiles.

any hints?

axum version

0.7.4

[jplatte]

Json must be the last extractor in the handler function signature: https://docs.rs/axum/latest/axum/extract/index.html#the-order-of-extractors