I'm creating an automated action in order to launch an activity for the purchases manager when an RfQ reaches the minimum amount for the vendor. 

This is my action 

And this is the domain expression (2 versions)

(1) 

["&","&",["state","=","draft"],["partner_id.x_mdg_minpurchase","!=",0],["amount_untaxed",">=", "partner_id.x_mdg_minpurchase"]]

(2)

["&","&",["state","=","draft"],["partner_id.x_mdg_minpurchase","!=",0],["amount_untaxed",">=", partner_id.x_mdg_minpurchase]]

The first doesn't work. The second raises the message "The domain you entered is not properly formed"

Can I compare 2 fields in the domain expression? How?