Cannot refer to both complete sales order and single sales order item

What causes this issue?

The request contains a reference to sales order and sales order item but
only one of these references can be made.

System Response

Processing is terminated.

How to fix this error?

For the same sales order you can either
deliver the whole sales order by providing a sales order reference on
header level or
deliver single sales order items by providing sales order references on
item level.
The combination of both references is supported for different sales
orders only.

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.