Retrospective method calculations for Customer Volume programs

Summary:

Hi,

I need assistance in understanding retrospective calculations for the customer volume program. I have done testing as table below, imported 4 invoices one at a time (CSV files) with different gross amounts, the earned amount seems to be correct till the third invoice is 2960, which is the end of Tier4. However, after importing additional invoice# 4 for 31000, it is showing the earned amount as 3200 in the checkbook. How is the system calculating the earned amount if the total amount falls outside the tier limit?

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