PO item & & does not allow invoice receipt

What causes this issue?

No invoice can be posted for the order item which you entered.
This can have one of two reasons:
No invoice receipt is defined in the purchase order.
GR-based Invoice Verification has been defined in the purchase order,
but no goods have been received that can be invoiced.

How to fix this error?

Check your entry and acknowledge the message by pressing ENTER.
The document overview screen appears. Via <LS>New item</> ->
<LS>Purchase order</> you can enter a new purchase order and item number
if necessary.

Error message extract from SAP system. Copyright SAP SE.