WSDL SOAP Go语言

I am new to Go (golang) and I am doing a test for a SOAP-CLIENT but I am not successful, I am implementing the following code but I do not receive any data:.

Install:

go get github.com/tiaguinho/gosoap

My code:

package main

import (
    "log"    
    "github.com/tiaguinho/gosoap"
)

type LoginResponse struct {
    LoginResult LoginResult
}

type LoginResult struct {
    sid string
}

var (
    r LoginResponse
)

func main() {    
    soap, err := gosoap.SoapClient("https://demo.ilias.de/webservice/soap/server.php?wsdl")
    if err != nil {
        log.Fatal("error not expected: ", err)
    }

    params := gosoap.Params{
        "client":   "asd",
        "username": "asd",
        "password": "asd",
    }

    err = soap.Call("login", params)

    if err != nil {
        log.Fatal("error in soap call: ", err)

    }    
    soap.Unmarshal(&r)
    if r.LoginResult.sid != "USA" {
        log.Fatal("error: ", r)
    }    
}

My Error:

2018/09/10 06:48:38 error in soap call: expected element type <Envelope> but have <br>
exit status 1

I do not know how to solve the problem, Thanks for your time and help