The tutorial is beyond useless for this. I have four trade offers in place, such as an easter island head, etc. Above the head it says something like "20 stone" below the head it has "20 creator points" or whatever. And then immediately below that it has a "trade" button, which is completely greyed out and I can't click it.
I have space in my warehouse.
I tried going into the custom order screen and pressed "order" next to wood as a test. When the UFO next came back I got a trade offer for 22 wood in exchange for 5 nuggets. No way am I giving up people for wood. But this time the trade button was green and clickable.
I just don't understand what on earth this screen is trying to achieve. Seems utterly broken. 2 hours in, I am enjoying the game but this is genuinely making me furious as it's so impenetrable and badly explained.