Goods receipt for PO & & only possible with ref. to outbound delivery

What causes this issue?

The "GI-Related GR" (goods-issue-related goods receipt) indicator is
active for the purchase order/purchase order item &V1&/&V2&. This
process allows the valuation type for materials valuated separately for
stock transport orders to be first entered in the outbound delivery at
the time of the goods issue and is therefore not defined at item level
in the purchase order. To ensure the consistency of the process and of
the material valuation, the goods receipt must then be posted with
reference to the goods issue or outbound delivery, or to an inbound
delivery that was created with reference to an outbound delivery
(message type SPED).

System Response

The system does not allow this posting because it could lead to
inconsistencies.

How to fix this error?

Post the goods receipt with reference to the outbound delivery or to an
inbound delivery that was created with reference to the outbound
delivery using message type SPED. You can create the goods receipt with
reference to the outbound delivery using transaction MIGO (goods receipt
for outbound delivery).

Procedure for System Administrators

If this goods movement has been posted using BAPI, IDoc, or
customer-specific applications, you must ensure that the correct
delivery is called and that the stock management unit, valuation type,
quantity, and base unit of measure have the same values as the goods
issue. For more details, see SAP Note 1677707.

Error message extract from SAP system. Copyright SAP SE.