Please enter a valid value for characteristic &.

What causes this issue?

You have entered an invalid characteristic value for a characteristic.

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?

Please enter a valid value for the characteristic. You can get
suggestions from the F4 help. If no information is available then it is
possible that no characteristic values exist for this characteristic.

Error message extract from SAP system. Copyright SAP SE.