There are many things that can stop a livery from appearing, and these are just a couple.
- A duplicate name in the title line in the aircraft.cfg. ie 2 aircraft liveries have the same value.
- An incorrect folder name in the aircraft.cfg.ie for texture, model or panel lines,
- An incorrect or msising entry in the layout.json for a crtical file. ie the fiel references an aircraft.cfg that doesn’t exist. Make sure you regenerate the layout.josn file after adding or removing any file, or after changing any folder names. I use this utility GitHub - HughesMDflyer4/MSFSLayoutGenerator: A drag-and-drop application for updating layout.json files in Microsoft Flight Simulator (2020) packages.
If you can’t work it out then upload your livery to your Google drive (or somewhere) and send me a personal message with the link to the file. I will have a look at it for you.