Element candy cannot be purchased from player shops.

So here's a weird thing I found.

I'm able to list element changing candy on my shop. alt text

The autosearch recognizes it. alt text

But searching brings up nothing. alt text

Put a shop terminal/counter in your room and see if it lists your light candy from there. Because on Ship 3, there's only one person selling Light Candy:

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And searching for an item I have up for sale won't show my listing unless I view it on my Shop Counter.

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So in short, the personal shop search won't show your own listings.