I got mine to seat, my previous repair eventually failed (sorry didnt take photos) and whilst squeezing them together I heard a click and it was good!
I think its possibly just a super tight connector. I would pull out the grommet with a pick, clean and lube everything and try again.
for future post viewers, I had this same problem the clips are fragile!
I ended up putting some heatshrink over it and before heating it, cable tie the connectors tight together, then heat up. I left the cable ties on but could probably remove them. It worked well, no more error and was easier...
Where are people getting the reverse signals from for a 7-pin adapter? Is this not also a PCM signal or can you just tap into the tail lights for this one?