I have taken the strixhaven feat for the chromatic orb spell in its list for my tempest cleric but cant make it function with higher level spell slots, am I missing something or what?

You choose two cantrips from fire bolt, prestidigitation, and ray of frost, and can choose one 1st level Bard or Sorcerer spell. Once per long rest, you can cast the chosen 1st-level spell without a spell slot. You can also cast it using any spell slots you have.

Feats cannot add spells that can use spell slots. You will either need to do the mental math for the damage and use the custom dice roller (if you use rolling on the sheet) and just check the spell slots off manually.

Or, you can make a homebrew copy of your race or subclass and add a hidden feature that adds the spell (counts as known: no, always prepared: yes, uses spell slot: yes).