Making a post from yew, version 0.19

Hi, has someone tried to make a post from Yew Framework to the back (actix , this part is working) with version 0.19?, sending data in a json format. I have some problems to send it with "wasm_bindgen_futures", that's what doc says.
I have this error:

panicked at 'called `Result::unwrap()` on an `Err` value: JsError(JsError { name: "TypeError", message: "Failed to fetch", js_to_string: "TypeError: Failed to fetch" })'

with this code

let data = Fields {
   name: "name".into(),
   phone: "999".into(),
   email: "".into(),

let data_serialized = serde_json::to_string_pretty(&data).unwrap();

wasm_bindgen_futures::spawn_local(async move {
  let post_request = Request::post("")
    .header("Content-Type", "application/json")