Contract &1 does not have any fitting items

What causes this issue?

A contract can only be used here if it has at least one item fulfilling
the following conditions:
The contract item is of product type Service
Receiving plant:
The receiving plant in the contract item is the same as in the purchase
order item or
The receiving plant in the contract item is empty
The contract item has the same material group as the purchase order item

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

System Response

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.