Down payments exist for this purchase order

CAUSE&
Financial accounting has made down-payments for the purchase order to
which the invoice refers.

System Response

The payment program automatically offsets the down-payments against the
payments to be made.

How to fix this error?

If you want to explicitly allocate a down-payment to an invoice, you
must make a manual transfer posting. To do this, choose the function
<LS>Invoice verification</> --> <LS>Environment</>
--> <LS>Clear down payments</>.

Error message extract from SAP system. Copyright SAP SE.