"Customer payment" field in the policy overview displays the overview of how much the customer has paid for the installments, how much is still needed to pay, and the overall policy balance. First, when there are no invoices or payments linked to this policy, the overview is displayed like this:

Whenever any installments are added or edited, or the gross premium changes, the figures here will be updated as well.

When any payments are linked to the installments, the paid amount will be shown in this section as well:
​

If any of the invoices are due, but have not been paid yet, there will be an extra line added showing the sum which is over due date. 

Note: Sum will be displayed as overdue even if there aren't any invoices created, but the installment period has started.