Ring Video Doorbell 3 Plus - Missing items?

I’ve got the Ring Video Doorbell 3 Plus, but there is neither no level nor backplate in the package. Why is this? I need to install the doorbell on a vinyl siding, and it’s not curved, sloped, or overlapping, so I don’t need to use the corner wedge already provided. I just want to install it on a vinyl siding that is completely flat (it’s like a vinyl column). Which screws do I use? Thanks!