The Manusya Coat of Fending when added to glam chest shows red X on job that can use it. Screenshot:
https://i.ibb.co/j3vQ9Ys/nogood.png
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The Manusya Coat of Fending when added to glam chest shows red X on job that can use it. Screenshot:
https://i.ibb.co/j3vQ9Ys/nogood.png
It's likely that the armour piece you're trying to glamour it onto is a lower level than that one.
Yeah, it sucks. What you can do though, is put it in your glamour dresser, apply it to a plate, then remove it from the dresser and equip it. Then you'll be able to use it for your glamour and not have to deal with putting it back in the dresser once you're not wearing it anymore.