Complete newbie to datapacks

Hi so I'm trying to recreate the Naked and Afraid SMP as a datapack. I.e wearing armor (other than skulls and elytra) causes damage to players, no health regen and so forth.
But I'm struggling to run commands that detect players wearing armor with these conditions.
I've even boiled it down to this "/execute as @a[nbt={Inventory:[{Slot:103b,id:"minecraft:air"}]}] run say Hi" and I cant even seem to get this to work haha.
If anyone is available to help it would be greatly appreciated