Deliv. note does not refer to PO item with GR-based inv. verification

What causes this issue?

The system cannot find a purchase order for the delivery note. This may
be due to one of the following reasons:
The purchasing department has not defined GR-based invoice verification
for this purchase order.
The delivery note number was not entered (or was entered incorrectly) at
goods receipt.
You have entered the wrong delivery note number.

How to fix this error?

Check the delivery note number and correct it if necessary. If your
input was correct, you cannot enter the invoice via the delivery note
number. In this case, proceed as follows:
If the invoice contains a PO number, enter it as a selection criterion.
If the invoice does not contain a PO number, position the cursor on the
field <LS>Purchase order</> and press F4. You can display all purchase
orders for this supplier. By referring to other data contained in the
invoice (such as quantity and price), you can find and selelct the
relevant purchase order from this list.

Error message extract from SAP system. Copyright SAP SE.