If I say to you "invisible pink unicorn" or "spherical cube", I would characterise myself as not having successfully meant anything, even though, if I'm not paying attention, it feels like I did.

In both examples I understand you to mean two (non-existent in the real world) items with a set of seemingly contradictory characteristics. So you did mean something. Not an object in the real world, but you meant the concept of an object containing contradictory characteristics, and gave examples of what "contradictory characteristics" are.

Indeed that meaning of contradiction is the reason "Invisible Pink Unicorn" is used to parody religion, etc.

Now if someone used the words without understanding that they are contradictory, or even believing the things in question are real -- they'd still have meant something: An item in their model of the world. They'd be wrong that such an item really existed in the outside world, but their words would still have meaning in pinpointing to said item in their mental model.