Unable to /summon potion with tag

We're unable to summon a potion with prepared data. Everytime the potion will be the Uncraftable Potion.

I don't know which one would be corret since none of them work.

/summon minecraft:potion ~ ~4 ~ {Potion:"minecraft:harming"}

/summon minecraft:potion ~ ~4 ~ {Item:{id:"minecraft:splash_potion",tag:{Potion:"minecraft:harming"}}}

For arrows through, everything works just fine.

/summon minecraft:arrow ~ ~4 ~ {Potion:"minecraft:harming"}