a little more information might be needed. probably would need to know the sp chip you are using, what type board you have, 10 meg (has volume adjustment knob on the top of it) or a 16 meg board, no volume knob. some sp chips require a certain dip switch setting, the same menu you entered to get to #8, begins with the 5_0-1-2, this setting is how the machine will handle payouts, the #8 setting will handle the inserted money credits, either put them on the display to be played down or paid out from the hopper, like a bill changer.
if all settings fail, and no matter what you try, check the wiring for the cash out switch, it is wired differently from the other switches, if wired incorrectly, it will cause the problem you are having.
as for the set chip, since the bill unit is working, all your settings that require a set chip are correct, you should have a set chip on hand just in case.
hope this helps
Jim