As you can tell, it uses a join event. You need to see the join event to be able to trigger it first.
If you have seen a join event in the channel, make sure that the script does not have another join event triggering prior to this script.
You'll need to open a new file in the scripts editor and paste the script in there for it to work in this case.
This is very likely the case if for example you're using a points system that uses a join event.
