The a lot of upcasted spells that doesnt consume spells slots.
Magical itens, innate spellcasting and still works pretty well without spending a single spell slot.
4th level fireball requires 4 Sorcery Point. its clear as water
So, let's walk through this one more time:
1) Sleep is a 1st level spell. I know this because I look in the spell lists and it's there under first level spells.
2) To make Fireball a higher level spell, the only way available is to cast it in a higher level slot. To do this, you must cast the spell using the cast a spell action and expend the higher level spell slot. Only then do we treat the upcast spell as a higher level.
3) The Psionic sorcery feature is an alternate mechanic from how spells are normally cast.
4) To use the Psionic sorcery feature, I select an eligible spell and can cast it directly from sorcery points, using as many points as the level of the spell.
Example: I can cast Sleep, a 1st level spell, using a 4th level spell slot. When I do this, Sleep becomes a 4th level spell only for this casting -- I must expend the 4th level spell slot and successfully cast the spell for Sleep to become a 4th level spell.
Okay, these are the rules above. Let's look at how you're doing it:
a) You desire to cast a 4th level fireball. You do not expend a higher level spell slot, but instead imagine that you could do so if one were available.
b) You then use 4 sorcery points to cast this imagined higher level spell.
This doesn't work, because you've created an entirely new way to make spells higher level -- you just imagine them as being cast using a spell slot that doesn't exist, and then pay for this imagined spell slot. That's not how it works, though, you actually have to both have and then use the higher level slot for a spell to become a higher level. Imagining that you could do so is not sufficient.