Segment & is used as reference segment in one extension

What causes this issue?

The segment &v1& is used in the extension &v2& as a reference segment.
Since the basic type &v3&, which you are editing, is already being used
to form an IDoc type together with &v2&, you cannot delete this segment
from the basic type &v3&.

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?

First delete the relevant reference segment in the extension &v2&.

Error message extract from SAP system. Copyright SAP SE.