Material &1 has not been created in plant &2

What causes this issue?

You have tried to assign a material to a rack meter that has not been
created in the plant assigned to the rack meter.

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?

This material must be created in the correct plant before it can be
assigned to the rack meter. You can extend materials using the change
material transaction in materials management.

Error message extract from SAP system. Copyright SAP SE.