Exactly like other users mentioned, you either have to create pedalternatevariations.meta or edit .ydd and add bone which is probably missing in your addon hair.
Probably first option will be better if you have no idea how to edit .ydd’s (you can copy any “empty” .ydd that is already in GTA) and create pedalternatevariations.meta file (I think there isn’t any tutorials how to do such, you would have to find out by yourself). But be careful with that .meta file, unfortunately using it to a lot of hairstyles might be a problem (I’ve tried using it once, and about ~80k lines will crash your game - it is like x4 more than any original file has)