It just took a very long time for the wardrobe to register this item is in it. It now shows up with a tick and the message that the item is in my wardrobe.

This is what my outfit should look like Outfit Not Found

The Pure Perfume Bottle isn't showing up on the site, though.

(1) When I do an account search is shows up as 1 found in your Wardrobe | (Remove One).

(2) When I do a wardrobe name search selecting Only show items you own it shows up.

(3) When I hover over it in the list of items on my HA it doesn't have a tick to say this item is in my wardrobe - there's just Search Shops.

It was definitely a cache thing in the end.

Glad it was that simple xD locking as resolved!