workday rest api testing

[deebee1234]

I have a questions.

I have rest api endpoint when I invoke the following url on postman

(post) https://impl-XXXXX.wd12.myworkday.com/ccx/oauth2/YYYYY/token  by passing client ID, secret and refresh token I get access_token.
in the body I pass:

grant_type=refresh_token&refresh_token=refersh_token_given_by_Workday_admin

I get bearer token

when I call
(get) https://impl-XXXXX.wd12.myworkday.com/ccx/api/v1/YYYYY/workers

and pass the access token as Bearer token I get 

{

    "error": "permission denied",

    "code": "S22"

}

I have ISU user created, I tried passing that user's cred as "Basic Auth" but I get 

{

    "error": "Unauthorized"

}

Can you direct me what mistake I am making or if there is any new permission is needed. 
Under domain security I have access to Personal data, worker data : staffing, worker data: workers and integration security.