Why are 10% of my payout withheld every month?

Every month, we withhold 10% of your delivery credit payment until the next month (§5 art. 3).
There are two reasons for this:
1. Security: In case a high number of products are being returned.
2. Cash flow: Amazon pays us with a delay of one to three weeks. That’s why we’re essentially paying our customers in advance for every product sold after the 23rd of each month – so we use the 10% as a financial cushion.
Here’s an example:
In August, we would have to pay you 100€. We keep 10%, as agreed upon in the contract.
In September, we add these 10% or 10€ of the previous month to this month’s payout – but again keep 10% of this sum.
That’s why it’s not possible to track with simple multiplication. You can therefore see the 10% in your overview of withheld payments.