Purchase order contains a value without a qty

What causes this issue?

The system found that the purchase order contains an item with a
purchase order value in document currency, but which does not have a
corresponding purchase order quantity.

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?

Check the item in the purchase order.
Do you want to
<DS:TRAN.ME23N>Display purchase order</>?

Error message extract from SAP system. Copyright SAP SE.