Item &1 does not relate to a main item

What causes this issue?

Contract items are above the fields <DS:DE.VTPID_KK>External GUID of
Provider Contract Item</> and <DS:DE.PAPID_KK>External GUID of
Higher-Level Provider Contract Item</> in a hierarchical relationship.
The root of the hierarchy is an item where the field <ZK>External GUID
of Higher-Level Provider Contract Item</> is blank or zero.
Contract item &V1& does not relate to any <DS:TX.FICA_INFO_FKKVTHIER>
main item</>.

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?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.