i am getting 401 unauthorized response : 
getThingsApi() {

    let uri = 'https://testapiserver/api/things/';
    let req = {
      method: "GET",
      headers: {
        Authorization: 'Basic cC5qYWltdXJ1Z2FuLm1jYUBnbWFpbC5jb206MTIzNDU2',
      
      }
    };
    console.log('InputRequest::' + JSON.stringify(req));
    fetch(uri, req)
      .then(response => response.json())
      .then(responseJson => {
        console.log('ResponseAxis::' + JSON.stringify(responseJson));
      })
      .catch(error => {
        console.log("Error::" + JSON.stringify(error));
      });
}

when i run above code , its working fine codesandbox.io..but not working in react native app.

Could you please suggest me..what i did wrong..