Does anyone have recent experience with applying a United GPU on a LH flight operated by PrivatAir? I'm having an issue and need an assist.

I booked a Q fare so I could be GPU eligible according to the Lufthansa requirements, but after booking when I tried to apply the GPU, it said that I am unable as the NBO-FRA flight on PrivatAir is "Region Restricted". I've searched and cannot find any info on lufthansa upgrade regions when it comes to GPU usage.

The 1K line was very helpful, but the feedback from them was that GPU's are only valid on Lufthansa mainline flights which I'm not so sure is correct. I saw a few posts on here that counter that information, so I wanted to check with FT folks to see if anyone has done this recently. What should I do next? Call LH?

I'm traveling NBO-FRA-IAH, Q fare.

Thanks!