I've followed this tutorial and running this code. File and folder creation examples work fine. But example to "Retrieve file contents", "Creating file under a folder" doesn't work. They keep giving error message like this: "DriveId is not found. Are you authorized to see this file". I've made sure that the "EXISTING_FILE_ID" does exist (first, created a file and then used its file id to retrieve contents). I'm not sure what am I doing wrong.
Anyone out there got these examples working ?