Can't Socket a spell gem into elemental invocation or cast on shock

Trying to socket the spell charged staff into elemental invocation or cast on shock but I cannot, says its a spell gem just like freezing mark. Both skills have the attack tags as well, unsure if it is a bug or just not worded correctly on elemental invocation and cast on shock. If it's not a bug would love you to change the wording for elemental invocation and cast on shock or charge staff.

Came to post similar. Was planning my first build to have Charged Staff socketed on Cast on Shock, but won't let me. Tags and wording indicate this should work; really hoping it's a bug that it doesn't.

I believe it doesn't work with any gem that is supposed to trigger spells even though the tags would imply it should work.