Can't attach object to Metahuman

Just experimenting with Metahumans, and I’ve loaded one into my level.
I though I’d be able to attach an object (e.g. sunglasses) through the pop-out menu, but the Metahuman doesn’t show up in the list of things I can attach it to.

If I use the eyedropper, I’m getting an error saying that the Metahuman is |“incompatible.”

No idea how to troubleshoot this… any help appreciated.