Has anyone used Copy opportunity Mapping to copy Related Custom object

Content

Created a custom Copy opportunity Mapping.

Added Related Custom Object in Entity Mapping : 'To' attribute shows the Relationship name created.

Opportunity>Customobject(RelationshipName). Hence,Selected this  and Query Type is 'Unique Identifier' and QueryAttribute is opportunity Id

And, mapped few of the custom attributes.'

It's not copying the custom object. Expectation is to create a new custom object record and create the Relationship with the copied opportunity using the mapped attribute values.

Has anyone tried this? Any pointers would be helpful.

Thanks

Nazim