Yes I was confused about this because at the end it said something like the string containing letters a - z I was very confused about what was being asked

Thanks for your time considering my work :)

Did you read the other comments?

The description says: "For one kind of boxes the printer has to use colors which, for the sake of simplicity, are named with letters from a to m." So these are the good letters, other letters are mistakes.

try changing the method accessor:
public static String greet(String name){...}