If system does not find given meeting room ID then it will give same error. So I suggest to use any other unique room ID.https://www.tutorialspoint.com/whiteboard.htm

You can use Advanced IDE to use multiple files. Here is the link:https://www.tutorialspoint.com/online_java_compiler.php

There are multiple sections in coding ground. Please go at the bottom and check advanced IDE section and there you will find old version of Coding Ground which still allows to use multiple files.https://www.tutorialspoint.com/codingground.htm