How can I upload a .json/.csv file using POST method with Rust in Yew framework (0.18)

Question

Here are my codes, the uploaded file are stored as self.file (which is an Option that converted to String using .into_iter()). But using .into_iter() cause an error stating:

`FormData` is not an iterator
the following trait bounds were not satisfied:
`FormData: Iterator`
which is required by `FormData: IntoIterator`
`&FormData: Iterator`
which is required by `&FormData: IntoIterator`
`&mut FormData: Iterator`
which is required by `&mut FormData: IntoIterator`
`js_sys::Object: Iterator`
which is required by `js_sys::Object: IntoIterator`
`&js_sys::Object: Iterator`
which is required by `&js_sys::Object: IntoIterator`
`&mut js_sys::Object: Iterator`

Here are my codes:

Msg::RequestCreateRecordsData => {
    //LOADING STATUS KE STATE
    self.loading = true;
    ConsoleService::info(&format!("DEBUG loading status : {:?}", &self.loading));

    let form_data = FormData::new().unwrap();
    form_data.append_with_blob("file", self.file.as_ref().unwrap()).unwrap();

    let mut body = String::new();
    for entry in form_data.into_iter() {
        let (name, value) = entry.unwrap();
        let entry = format!("{}={}&", name, value);
        body.push_str(&entry);
    }
    body.pop(); // Remove the trailing '&'

    let url = format!(
        "https://test-dps-api.dev-domain.site/api/document/{}/{}",
        &self.props.app_id,
        &self.props.card_index
    );
    let request = Request::post(url)
        .header("Content-Type", "multipart/form-data")
        .body(Ok(body.into()))
        .expect("Could not build request.");
    let callback = 
        self.link.callback(|response: Response<Json<Result<String, anyhow::Error>>>| {
            let (meta, Json(data)) = response.into_parts();
            match data { 
                Ok(dataok) => {
                    // ConsoleService::info(&format!("data response {:?}", &dataok));
                    Msg::Ignore

                }
                Err(error) => {
                    Msg::ErrorIgnore
                }
            }
        });
        // self.callback_toggle_insertrecord.emit(Msg::ToggleInsertRecord);
        let task = FetchService::fetch(request, callback).expect("failed to start request");


        self.fetch_task = Some(task);
        ConsoleService::info(&format!("Getting Data.."));

    true
}

I've tried to change it to .entries(), .to_string() and .into() and nothing helped. Any help from you guys would be muchly appreciated!