I am trying to search for carved pumpkins to add to my wishlist, however whenever i do it pops up as "invalid item" on the top part of the screen, I've tried other search terms/words too and the same happens.

What are you searching? As far as I know, it has to be the exact name of an item you're looking for (it doesn't work like vault where it show you everything that contains that phrase). For example, you can't search "Carved Pumpkin" but you can search "Priggle Carved Pumpkin"

Yeah, the Item Directory only allows searches for exact items names. I wish it could be changed, but it seems unlikely to happen any time soon.

I would recommend using Subetalodge to search for things like that instead, they have links with items to do an account search and stuff, so you can still figure out what you need relatively easily.