Casement Window Won't Latch
Thanks for your patience during this busy season. At a glance, it appears that you window is missing its tie bar. This is a long, flat bar that the lock arm clips onto. When you throw the lock, the tie bar moves up and down, engaging or disengaging with the keepers on the sash (that plastic part in your first photo).
We sell a ton of tie bars, but the problem here is that we have no way to know what you have without seeing the original as a reference. They come in a vast variety and it's not something you can really guess. A physical reference is necessary.
Do you have an identical window elsewhere in the house? If so, we can use that as a reference. In the meantime, you can see our full selection of tie bars here.