Post Request with strings.NewReader Containing Escape Sequence

I'm trying to retrieve a response from a POST endpoint which accepts a payload.

For curl request:

curl --request POST \
  --url https://api.io/v1/oauth/token \
  --header 'Accept: application/json' \
  --header 'Content-Type: application/json' \
  --data '{
      "userToken": "myemail@domain.com:MyUserProfileToken"
    }'

I can do this with:

func GetJWT() string {

    endpoint := "https://api.io/v1/oauth/token"

    payload := strings.NewReader(`{
      "userToken":"myemail@domain.com:MyUserProfileToken"
}`)

    req, _ := http.NewRequest("POST", endpoint, payload)

    req.Header.Add("Accept", "application/json")
    req.Header.Add("Content-Type", "application/json")

    res, _ := http.DefaultClient.Do(req)

    defer res.Body.Close()
    body, _ := ioutil.ReadAll(res.Body)

    return string(body)
}

and

    payload := strings.NewReader("{\n  \"userToken\": \"myemail@domain.com:MyUserProfileToken\"\n}")

However, when I try to pass string pointers for email and token, and declare the payload like

func GetJWT(userEmail, userToken *string) string {

    endpoint := "https://api.io/v1/oauth/token"

    payload := strings.NewReader("{\n  \"userToken\": \*userEmail\":\"\*userToken\n}")

    req, _ := http.NewRequest("POST", endpoint, payload)

    req.Header.Add("Accept", "application/json")
    req.Header.Add("Content-Type", "application/json")

    res, _ := http.DefaultClient.Do(req)

    defer res.Body.Close()
    body, _ := ioutil.ReadAll(res.Body)

    return string(body)
}

an error is returned for unknown escape (column 53 on payload declaration).

How can I escape string pointers so that I can concatenate userEmail, ":", and userToken