FBA Discount completely wrong. Help.

Hi Support,

In the meantime, I'd like to run my head against the wall and ask, how is it possible to stay profitable if Amazon keeps breaking its promises? I found one day that I was surprisingly given an FBA fee discount per unit of $4.28. A few were on sale during the discount, and I decided to see if the discount was valid. As you can see from the picture, 2 units have been purchased from me, and the FBA Discount per unit is $4.28. Even so, I have only been given a $4.28 discount for two units. If the FBA Discount per unit is $4.28 and they bought 2 units at once, why isn't the total discount $8.56?