Is this something that I don't understand or it's an unfinished mechanics that's yet to be implemented?

I agree, in the below screenshot.. what is being proposed to me?

Yeah - at this point I have to believe that the diplomacy and trade feature of Humankind is not fully implemented in this openDev.  There are some great aspects to it, and some that seem broken or completely missing.  

I definitely plan to report on it when I finish a game.

Right now when it's accepted, it's like all the demands are forgiven. So i just refuse all defusal.

I assumed you were not being offered anything in return because there was nothing in 'treaties' or whatever