You cannot edit conditions in the case of free goods

What causes this issue?

This item is for free goods. Since items of this kind are valuated at
zero, it does not make sense to enter or display condition values. The
system therefore does not allow this.

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?

Error message extract from SAP system. Copyright SAP SE.