I've just figured it out.
There's a 'My Transactions' section within the Credits page.
I deleted a photo, which cost me 10 credits. So creators are encouraged to keep content on the platform, I get it now :)
And I 'unliked' a post, which cost me 1 credit.
I pressed on the 'like' again after 'liking' it because I wasn't sure if I had liked it already, so I ended up 'unliking' it that way.