Would you mind posting your code here (and marking it as a spoiler)? That way, I can potentially identify and locate the problem, cheers :)

Great work! You may want to explore a feature called regular expressions to understand other people's solutions for this kata.

https://stackoverflow.com/questions/11502052/throwing-strings-instead-of-errors

Being able to throw an Error (once again, an Error, not a string) is important because if, for example, you receive a wrong type of input you want to clearly identify that the input was wrong and that your code is not supposed to work with this input. Imagine you were asked to input your name and instead typed up some numbers: you would expect an alert message telling you that you did something wrong. That is why it is a better practice to program error throwing instead of accepting wrong inputs.

Make sure you are throwing an Error, not a string. See the link below in answer to james1968.