Confirmation control key is not entered in purchase order item &1 &2

What causes this issue?

No confirmation control key has been entered in the purchase order item.
A confirmation control key is required in the purchase order item so
that the corresponding inbound delivery can be created.

System Response

The purchase order is not created.

How to fix this error?

Check the following settings:
Document type for the purchase order: is the vendor data included?
Vendor master: does the vendor master contain a confirmation control
key?

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.