Always get 'insufficient permission' when I try to get file/folder information via Box API

Hi,

I am an employee having trouble getting file/folder information via Box API. With enterprise admin's help, I created an authorized App and created an AppUser. Using server authentication, I was able to create folder, upload files into the folder, and add collaborators into the folder. However, when I tried to get folder information, I always received 'insufficient permission' error. As a comparison, I created a new folder and got folder information immediately. The error was still there.

Following functions were used in this work:

1. to get access token:

2. folder operations:

3. The script used to get folder information:

I always saw

{"type":"error","status":403,"code":"access_denied_insufficient_permissions","help_url":"http:\/\/developers.box.com\/docs\/#errors","message":"Access denied - insufficient permission","request_id":"qgn0b0flyhmimv2c"}

What permission do I need to get folder/file information? If anybody encountered similar issue, please please please share your experience.

Many Thanks!

Yi