How To Fix STGR123 - Plant &1 is already a purchasing reference plant

SAP Error Message - Details

• Message type: E = Error

• Message class: STGR - Hold store grouping messages

• Message number: 123

• Message text: Plant &1 is already a purchasing reference plant

What causes this issue?

The plant that you want to assign to a reference plant is already a
reference plant itself with its own assigned plants.
A reference plant cannot be an assigned plant.

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?

Select another plant using help list.
If you really want to assign an existing reference plant to another
reference plant, you have first to unassign all its assigned plants.
The reference plant will automatically become a normal plant and then
you will be able to assign it to another reference plant.

Error message extract from SAP system. Copyright SAP SE.