Packaging material type &1 is not assigned to packing group &2

What causes this issue?

According to Customizing settings, this material cannot be packed into
the packaging material.

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?

Assign the packing group to the packaging material type, or choose a
different packaging material.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.