SP872 (or SP0872) has a setting with a DIP switch on the MPU board which will force all bills to pay out of the hopper if the switch is flipped. With the power OFF, remove the MPU board from the machine and ensure that DIP switch 4 is set to "OFF". If DIP switch 4 is set to "on", all bills pay out of the hopper no matter what.
Next, go into the self-test settings (no SET chip required) and see if you can now change option 8 to 1. Also while you're there, ensure that option 5 is set to 0 (standard credit/noncredit) or 2 (player-initiated noncredit).
I have attached the PSR for your SP872 chip. I have also attached Ron (r273's) "for rookies" spreadsheet which helps walk you through the different settings in your machine. The SP872 isn't in there, but the SP874 is, which is from the same generation of chips -- the instructions there should apply to the SP872. Note that it does mention in the sheet that the SET chip is needed to change option 8. I believe that may be an error -- the PSR does not state that the SET chip is needed to change that option.