The only problem I see there is that you're using $2. In this case, it should be $1.
When using an alias, the first "word" after the alias name will be $1. The second "word" will be $2. And so on. So, you use GAdmin nick. The first "word" is the nick, so that will be $1. In the example I gave before, the channel was the first "word" and the nick was the second. That's why the channel was $1 and the nick was $2 in that specific case. And each "word" is anything separated by a space.
Think of $N's as words. $1 is the first word, $2 is the second, and so on. If you were to write a sentence "This is a sentence.", then you have $1 through $4 there. Now, this is the case when using a space character as the separator. Space is used for aliases and is the default for events like on TEXT. However, if you had a list of items, such as "car,truck,boat", there aren't spaces there, so that is all in $1 if you use spaces to separate the "words". For this, you could use /tokenize and instead of using the space character (chhr 32), you can use the comma as a separator (chr 44). After using tokenize with a comma as the separator character, car would become $1, truck would be $2, and boat would be $3 even though there aren't spaces.
You can find out more information on how tokens work with:
/help /tokenize
/help token identifiers
Although identifiers like $gettok() use just the number without a $ before it (1 instead of $1) when selecting the "word", it is the same concept, so should be helpful in understanding what's going on.
