Volume offers -- Off Invoice -- Discount is not applying on accumulated volume.

Hi Channel Revenue guru's

I am finding an issue with Volume offers  -- please check below details and provide your suggestions

Volume offer --- Incentive: Off invoice

Market Eligibility: 2 customers are included with group number 10 and 20. -- Retro flag enabled and Combined flag is enabled.

Discount level: Group of lines

Pricing phase: All lines adjustment

Quantity Range  - Discount % 

0 to 10 -- 2%

10 to 20 - 5%

20 to 9999 - 10%

Expectation:

When i enter an order line with 11 units -- the discount should be at 5%

when i enter an order line with 21 units -- the discount should be 10%

when i enter additional orders -- when cumulative volume is more than 21 --- the discount on all future orders should be 10% etc.