Google Contacts API中使用的Google Data语法正确的Content-Type是什么？

I need to read and update the Google Shared Contacts in a G Suite domain using Golang. Since there is no existing Go client library for this API, I'm having to interact with the API at the http level. Presently, I'm stuck on sending the correct Content-Type header.

Since the documentation at https://developers.google.com/admin-sdk/domain-shared-contacts#Creating says to use application/atom+xml that was naturally what I tried. However, the response I receive is a 406 Not Acceptable with a body message of "No acceptable type available". Omitting the Content-Type returns a 400 "Response contains no content type". Using text/xml returns a 415 with "Content-Type text/xml is not a valid input type."

    req, err := http.NewRequest("POST", href, bytes.NewBuffer([]byte(body)))
    if err != nil {
        return "", err
    }

    req.Header.Set("GData-Version", "3.0")
    req.Header.Set("Accept", "application/json")
    req.Header.Set("User-Agent", "personnel-sync")
    req.Header.Set("Content-Type", "text/xml")

    resp, err := g.Client.Do(req)
    if err != nil {
        return "", err
    }
    defer resp.Body.Close()

    bodyBytes, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatal(err)
    }
    bodyString := string(bodyBytes)
    log.Println(bodyString)
    log.Println(resp.Status)

    return bodyString, nil

The body I'm sending is the example in the documentation (link above) but it doesn't seem to matter at this point because an empty body gives the same response.

Barely a minute after posting the question I spotted the problem. Sure enough, it wasn't the Content-Type header, but the Accept header. Removing that solved the problem. To be specific, Google was complaining that I requested application/json as a response type. The Accept header is apparently not even required.