Http post return NULL

Ionic Framework ionic-v3
1

Hello.
I’m trying to get the results of the post request and Ionic returns null. Postman returns valid json.
What’s my mistake?

this.httpClient.post('http://devel.do-kirov.ru/app_vyatsu/login',
      JSON.stringify({ username:  encodeURIComponent(this.username), pass: encodeURIComponent(this.password) }),
      { headers: new HttpHeaders({
        'Content-Type': 'application/json'
        }),
        responseType: 'text' })
      .subscribe(
        data => {
          console.log(data);
        },
        err => {
          console.log(err);
        });