REST API url to list specific folder content

I need to retrieve the items/documents in a specific folder of our Office 365 hosted SharePoint site, but I always get an resource error.

The url to the SharePoint site with the files is http://ift.tt/1BwoSTB

and according to the MSDN documents on this page, http://ift.tt/1CDpnLI the call should be

GET {base-url}/Files/{folder-id}/children

and "base-url" should in the case of SharePoint be

http://ift.tt/1BwoSTF

Now, I've tried 10 different combinations without getting any good results, so I guess I'm doing something wrong with the base-url or the site-path. Is the correct base-url this for my site

http://ift.tt/1HLFjwv 

or just

http://ift.tt/1BwoSTJ