It is very old, but it works with v2026. BUT there are several 'reverse face' tools available that are newer, less flaky, and probably better... e.g. my own 'Fix Reversed Face Materials' which flips faces textured on their backs and reapplies the material, UV-mapping any textures to suit, and includes several other subitem tools to adjust reversed faces and their materials...

I was suggesting that you contact them since you are using their plugin. I don't use it so they'd have no reason to help me with it. It would be better if you contact them directly so there's no one in the middle.