Let's assume that we give 1 reward points for every $10 in a shopping. (1 point = $1)
A customer made a $100 shopping and earned 10 points. This order is completed.
And then, he spends 200 dollars on his next shopping and he wants to use that 10 points.
He should normally pay $190 and earn 19 points.
Yes, he pays $190, but unfortunately he doesn't get any points.
Can you test this scenario?