You can only assign one value to characteristic &

What causes this issue?

You attempted to assign several values to characteristic &V1&. The
characteristic is configured in the classification system for single
values.

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 only one value to the characteristic.
If you need to assign several values to characteristic &V1&, you need
to reconfigure its definition in the classification system.

Error message extract from SAP system. Copyright SAP SE.