The first is that you need to make sure that the 7 little plastic rivets are are not still in the locked position, you can tell the difference by looking at these two pics I blatantly stole from someone else's write-up. The first is of the clip in a locked position (not what you want), the second is the unlocked position which is what you are shooting for.
Apparently these things have a tendency to break or get stuck in the door, I guess I was lucky. Either way its probably best to pick up a couple spares form the dealership or whatever.