Amount in line will be set to zero

What causes this issue?

In an invoice item you entered a quantity of 0 and an amount not equal
to zero. This is not allowed.

System Response

Once you have acknowledged this messgae, the system will automatically
set the value to zero.

How to fix this error?

If the quantity should not be zero, choose
<LS>Correction on/off</> from the document overview and enter the
correct quantity and amount.

Error message extract from SAP system. Copyright SAP SE.