Contract cannot be uniquely assigned - use input help

What causes this issue?

The SRM central contract item entered is assigned to several SAP S/4HANA
contract items.

System Response

It is not possible to derive a unique assignment.

How to fix this error?

Either enter the SAP S/4HANA contract (outline agreement) as well, or
use the F4 help to select the contract item.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.