"401 Unauthorized" when sending HTTP request through javascript on POSTMAN (but not with a simple HTTP request)

for a url ${baseUrl}/users/${user.id}.json where baseUrl = ‘https://{subdomain}.zendesk.com/api/v1’

I was able to run PUT request on Postman to edit custom field in the data with ease.

The authentication method I used was 

[Basic Auth]

username: {email}/token

password: API token I generated

And yet, for a bulk update over the json data, (user list) using either of the script I am getting 401 error

1. pm.sendRequest({

    url: `${baseUrl}/users.json`,

    method: 'GET',

    header: {

        'Content-Type': 'application/json',

        'Authorization': pm.environment.get('auth')

    }

2.  ----the rest same----

   header: {

        'Content-Type': 'application/json',

        'Authorization': pm.request.headers.get('Authorization')

    }

Does anyone have advise? Thank you