Lightning Bolt MTX is not applying to skill

I purchased the lightning bolt MTX to use with the skill granted by Choir of the Storm amulet. The skill does not appear in the cosmetics menu and the MTX cannot be used. I have read in multiple places that MTX must apply to a skill gem and not skills granted by items. This is still confusing because there is no skill gem for lightning bolt currently in the game and the MTX can be used with the skill granted by Voltaic Staffs but not Choir of Storms. If this is the intended function then it needs to be stated before purchase as to not mislead others to buy something they cannot use.