Keep getting this error when I attempt to export the FBX, this model doesn't have any UV's. All it has are basic materials assigned (no textures) and rigging. I tried removing parts of the model and when I remove the highlighted segment type (in orange in the SS) the export works. But I don't understand why that segment is causing a problem. I have never had an issue like this before. This is on Blender 2.91. Does anyone know how to fix this?
Just a guess here:
I suspect this was based on something like the cube mesh, which comes with its own UVs even if you don't do anything with them, and that is what's causing this. Or maybe you built that side from scratch so it really doesn't have any UVs but everything else does, and FBX export is looking for a UV even though it won't end up being used.