No location can be determined in APO for plant &2 (customer &1)

What causes this issue?

The system was unable to find a location in the SAP APO system for plant
number &V2& of customer number &V1&.

System Response

The system cancels inbound processing.

How to fix this error?

Ensure that the customer number and plant number in the IDoc PROACT
contain suitable values. The customer number is expected in section
E1ADRE1 for vendors with the qualifier '300' or '301'. The system takes
the plant number from the section E1ADRM1 field PARTNER_ID for the
ship-to party.
Maintain the <ZK>master data</> so that it is suitable for VMI customers
(in the menu under Edit/VMI customer assignment). You must assign the
location for the ship-to party in the SAP APO system to customer &V1&
and enter the plant number of the customer as the external description.

Error message extract from SAP system. Copyright SAP SE.