If you are receiving this error, this would be caused by a vacancy with this reference being previously created within your system
In order to resolve this follow the below:
Click Access Button
then click ATS.
Select the Vacancy.
Click in to the Reference box and change the reference.
Select Save.
Go back to the new vacancy.
Input the desired text into the Reference box.
📌Note: If you deleted the vacancy that this reference was used for, it would not be possible to use this reference going forward.