I can tell you how to do it:
1) In the contract negotiation - propose the lower amount that comes up by default (or really low ball to make sure the player comes back with a reply)
2) The player will respond saying we can do better, etc.
3) BEFORE you hit the X button [PS4] to bring up the screen again to adjust the numbers - press and HOLD the down button on the D Pad. WHILE HOLDING THE D PAD DOWN - press the X button
4) You will now be have access to the list of items you couldn't get to before. It's starts at the bottom and you can edit each category working your way up.
PLEASE NOTE - you can't move back down once you move up to the next category - so make sure you know what you wan to propose before you start editing.
I hope that helps. This was literally a game saver for me *whew*