Not all mandatory partners could be determined automatically

What causes this issue?

You assigned a <DS:GLOS.partner determination procedure>partner
determination procedure</> containing mandatory partners to the
<DS:GLOS.order_type>order type</>. Not all of these mandatory partners
could be determined from the reference object when creating the
<DS:GLOS.maintenance_order>order</>.

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?

Check the reference object.
Maintain the <DS:GLOS.partner>partner</> in the created order.

Error message extract from SAP system. Copyright SAP SE.