It sounds like the service inside the PagerDuty account may have been deleted. Do you have access to the PagerDuty account that the ServiceNow instance is integrated with, and can you log in and check?
If the service associated with that assignment group is no longer there, then what you’ll need to do is re-provision, as follows:
- Modify the assignment group dictionary entry and disable the read-only flag from the fields “PagerDuty Escalation”, “PagerDuty Service” and “PagerDuty Webhook”.
- Modify the assignment group, removing (setting to empty) those three fields
- Provision the service by clicking on the button in the view of the assignment group
If you still have the escalation policy previously associated with the assignment group, you can set the PagerDuty Escalation field to its ID. It should be in the URL when viewing it in PagerDuty using a web browser; it should be a string of uppercase alphanumeric characters beginning with
Hopefully that helps!