So I figured out that he's not unlocked because I still need to trade in 27 more markets. He's making me do all this work I'm just gonna see Didi Vatermann instead!Hmmm....
a) do you have the invitation for Lei Cheung (from The Dweller)?
b) are you actually playing in Horizons or did you boot the base game instead?
You need both conditions fulfilled in order to be able to land there.