So you need to have T&T Emporium which is the final stage of the Nooks shop

Leif will have a section to buy fertilizer. You only get T&T Emporium by getting all the past upgrades of Nookling Junction AND
Spending 250K bells at TIY
Passing 4 Gracie Fashion Checks (She randomly will appear at the plaza on random days so it can take up to 5 years for all checks)
It must have been atleast a month that you have had TIY.
And you must have the garden center, shampoodle, and kicks open.
EDIT: You also have to pass Gracie's check with atleast satisfactory level meaning that 3 or more clothing items fit the breif. Here is a guide for when she appears in your town. Also this is a guide on how to get all shops if you dont have the others.
Gracie the fashionista giraffe may appear in your town square from time to time. She will assess your fashion sense.
www.thonky.com
I hope this helps!!
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