I had some trouble initially, also, but think I got it resolved somehow. I had manually downloaded a few skins from the BB links, put them in the skins folder, and they stayed in red text. SO I renamed the skins.res file, and noted like you, a new res file hadn't been created. So I renamed it back. I was able to get it to recognize the new skins, and also download and install skins by clicking on them in the hangar.
Still trying to download P51d_58.res every time I login, even it completes the download.
BTW my skins.res file is dated 10/27/23, which I think is the old file.
I was flying with the new skins last night, but they disappeared and had to re-D/L from the hangar this morning....