Hi, it’s been a while since I’ve completed this one, but it might be because the assignment is asking you to use require instead of throwing a custom exception.
Try using require to verify the argument you’re passing. Then you can return the [0] portion as you’ve done. I think having the require to verify your argument at the the beginning ensures you can always just return [0] as well, and nothing else would be needed. I think that should take care of it.
One other thing I noticed is that I’m not sure if your code would ever reach the return "No NetID found!" portion with how the current if-else statement is constructed.