I'm pretty sure I ripped that connection apart on a kerb (on this S8 and the previous one), so the garage screwing it together closely makes sense, there's not much hanging down now to catch next time.
But that's probably why there are 10 connectors in a pack.

Job done, though it's a pig to fit those little retainers as they have to be inserted from behind and squeezed to pop through the rectangular (near-square) hole.

Sod-all access, tough plastic popping back and crushing fingers, but makeshift tools and various spiky metal things helped get it done in a few minutes. Had to swing the steering from side to side a couple of times to improve access, but generally its easier with the wheel pointing in on the side you're fixing, which may seem illogical. The wheel out actually gets in the way of your arms which need to get into some strange positions.

For reference the holes in the undertray for the wheel-arch connection are "vertical" rectangles so the clips have to be squeezed sideways to insert from the back.
The retaining pins/pegs are then inserted with the slot horizontal and turned 90 degrees clockwise to lock with the slot vertical.
I found it best to insert the retainers at an angle so that the "ledge" on one side was caught then push from behind and squeeze against the other side until it popped in. Which side first depended on where and how you get access to squeeze, it was much easier on the inboard ones. And the nearside outboard one was the worst, I think there's just more "stuff" behind the wheel arch liner limiting access and movement.

Obviously the "correct" way is to have the car on a lift and fit all the retaining clips while the undertray is off the vehicle. Then fit the main metal supporting retainers and finally the plastic connectors at the edges.

I currently have 6 spare pins and 7 spare clips. And no intention of investigating the (currently screwed) front edge connection to the bumper.

Just a couple of pictures:
Nearside showing the OEM wheel arch liner pin (I replace the missing offside one) and the new outer undertray connector.
Offside showing both new inner (dark!) and outer undertray connectors at the front bottom of the wheel arch.

That's the ones I'm missing from various locations on the car. Just as well I ordered up 20 of them.