Cant get the root folder of the user from the admin api

 You can access a Managed User's content with an access token scoped to an Admin using the As-User Header. To specify the user's root folder in the Get Folder's Items call, set the folder_id parameter to "0".

I am trying to use admin client id ,client sercret,access token,refresh token)

BoxAPIConnection api = new BoxAPIConnection(cientId, cientSecret, accessToken, refreshToken);

 // for users inforamtion

api.setRequestInterceptor(new RequestInterceptor() {
            @Override
            public BoxAPIResponse onRequest(BoxAPIRequest request) {
                request.addHeader("As-User", "access-id");

                // Returning null means the request will be sent along with our new header.
                return null;
            }
            });

 BoxFolder folder=new BoxFolder(api,"0");

this still gives me 401 status