Cannot Redeem Coupon in OM

Hi,

I am trying to use promotional modifier - coupon issue with the steps provided in the Advance Pricing User Guide - Scenario 1, where the first purchase issues a coupon for 10% discount in the next purchase.

The first order shown that the coupon modifier was applied as expected, the flow is then completed to receivables. However, on the next purchase, the price won't change after I apply the coupon via the action button.

Are there any additional setup that are not written in the user guide that I might miss?

Thanks