Changes with history have been made to relationship type &1/&2

What causes this issue?

The history maintenance for relationships cannot be set to 'Maintenance
without History' again, because relationships of this type have already
been created with change numbers.

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?

Delete the relationships that you have created with change numbers for
the selected relationship type.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.