ConcealPro

We bought this 2015 S line a few months ago and just noticed something is missing from the rear bumper. Any idea what this part is

called so I can order one?

cuatrokoop

It's the panel where the hitch comes through...

JMAPUK

Yep it's one of these

AUDI Q7 10-16 REAR BUMPER TOW HOOK BAR COVER CAP GREY 4L0807819H1RR <-- part number eBay UK price genuine part £64

ConcealPro

Looks like that one is different than the S Line

cuatrokoop

Yes, S-Line vs non, face-lift vs early. So there are several options to choose from. If you can find your build sticker (spare tire well IIRC), you can look up the options installed at the factory, then it can be properly looked up.

2K1
2K2
VJ1
VJ4

2K7
2K8

VJ0
VJ2
VJ3
VJ5

2K9
2K6

Those are the four main rear bumper groups available in the USA for 2015. There are, of course, options inside those groups to narrow down the part number and color code of the part number (one part number can have multiple different color codes depending on options).

4L0807819H
4L0807819M
4L0807087B
4L0807819F
4L0807819P
4L0807819G
4L0807819Q

Those are the various base part numbers.

What you thought was a simple question, is not really that simple to answer...