Log. system & for APO not permitted when using external number assignment

What causes this issue?

The logical system &V1& was entered to create orders with external
number assignment. This logical system is the logical system to which
the SCM system is assigned.
External number assignment and the logical system entered are used to
determine from which external system an order was transferred to the SCM
system or to which external system an order belongs. For this reason,
the logical system entered here must not be the logical system of the
SCM system.
For more information, see the documentation for the parameters of the
<DS:DE.BAPIAPOLOGSYS>logical system</>.

System Response

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

How to fix this error?

Choose another logical system.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.