Amount & and quantity & not allowed

What causes this issue?

In the invoice item entered the quantity is 0 and the amount is not
equal to 0. This is not allowed. It is therefore not possible to post
the parked document.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Exit the <LS>Post parked document</> function. Choose the
<LS>Change parked document</> function to:
correct the quantity
or set the value to zero; you may have to add an additional line
so that the document balance is zero.

Error message extract from SAP system. Copyright SAP SE.