Main character is a boy who mucks stables (a job which has medical benefits) but dreams of being an enchanter making potions.
Boy's first potions fall flat (not having a clear theme or plot driver) but he keeps working late at night and early in the morning on his magic (and luckily, stable mucking is a mindless task.)
Boy makes a lovely potion, divides it into four vials and leaves family, heading to the city of glass and towers -- the city of the enchanters -- where he'll need to face one of the four Gatekeepers to get in (and sadly, the boy hasn't been able to afford a subscription to Gatekeeper's Weekly so he's not sure exactly what each Gatekeeper is looking for in a potion.)
On the way, he meets a baker, a milliner, and a minstrel who add things to three of the vials.
The boy submits the adulterated potions to the East, West, and South Gatekeepers all of whom send back a printed rejection note: "Dear Potion Maker..."
The boy submits his last vial to the North Potion Maker who also sends back a printed potion rejection note. But, 'Flop and Floption!' there's a handwritten note scrawled at the bottom:
Keep working, the trope of this magic is overdone, but your plot construction shows promise
WHAT WILL HAPPEN NEXT????