Internal error: Location type for location & in BSG & not unique

What causes this issue?

You tried to post stock in location &V1& in the business system group
(BSG) &V2&. However, the location type of this location does not allow a
stock posting. Stock postings are only possible for locations with
location types 1001 (plant), 1011 (vendor) or 1012 (customer).

System Response

SAP APO does not post the stock.

How to fix this error?

Check the location type of location &V1& in the BSG &V2&. Check whether
you have installed notes that implement new location types in the SAP
R/3 Plug-In. Check that all relevant SAP APO notes (component
APO-INT-STK) are installed.

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.