Did you get errors when you tried using that code?
I'm not even sure it would load at startup.
Some hints - (I don't like giving people out-right answers at first...doesn't always teach people to debug own code)
1) Your "if" statement has no "end"ing (you only have one "end" and it "end"s the function)
2) You don't need an if statement for the idea you're trying to use.
3) Your variable "v" doesn't exist. I understand you're trying to perform a command on a player object, but, you never tell lua what v is.
4) As written, your "target" is always going to end up being your "calling player". ULX command structure always passes the caller first, then other variables after...you used PlayerArg, so the second variable passed to your function is going to be your "target"; but you've set up your function to accept one variable, and it will be the caller (even if you name it target)
5) You don't necessarily NEED to use v, or tell what v is. You could just use the "target_ply" already passed into the function (ie, target_ply:SetClipboardText)
6) You'll need to research how to make sure this only runs on the client side or it won't work (though, running on server side shouldn't hurt, it just won't work)
Hopefully, enough hints to keep you going.