code: func (api UsersAPI) ValidatePhoneNumber(w http.ResponseWriter, r *http.Request) {
  	username := mux.Vars(r)["username"]
  	label := mux.Vars(r)["label"]
  	lang := r.FormValue("lang")
  	if lang == "" {
  		lang = "en"
  	}
  
  	userMgr := user.NewManager(r)
  
  	userobj, err := userMgr.GetByName(username)
  	if err != nil {
  		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
  		return
  	}
  
  	phonenumber, err := userobj.GetPhonenumberByLabel(label)
  	if err != nil {
  		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
  		return
  	}
  
  	validationKey := ""
  	validationKey, err = api.PhonenumberValidationService.RequestValidation(r, username, phonenumber, fmt.Sprintf("https://%s/phonevalidation", r.Host), lang)
  	response := struct {
  		ValidationKey string `json:"validationkey"`
  	}{
  		ValidationKey: validationKey,
  	}
  	w.Header().Set("Content-Type", "application/json")
  	json.NewEncoder(w).Encode(response)
  	w.WriteHeader(http.StatusOK)
  }
docs: // ValidatePhoneNumber is the handler for POST /users/{username}/phonenumbers/{label}/validate