If you are seeing a message stating Person not linked, this may suggest that the employee has been created in PeoplePlanner manually rather than via the integration driven by SelectHR.
It is recommended that you ensure that you are creating the employee in SelectHR and then adding them to the Rostering Link. This will automatically create the PeoplePlanner employee record for you.
If the employee has already been created, we recommend you terminate the record in PeoplePlanner and then make a change to the employee record in SelectHR. This should allow SelectHR to send the record via the integration to create them in PeoplePlanner.
Alternatively, you can remove and re-add them to the Rostering Link in SelectHR, which will have the same effect.