The exception “Error Occurred: This Route Work invocable action did not create a valid Pending Service Routing. Exception in Salesforce” might be due to following reasons
1. Check whether you are hard coding in Salesforce Flows.
For example, if you are hard coding Skill Id, Routing configuration Id, etc., then the Ids will be different across the orgs.
Double check the Ids used in the Route Work Action element. Make sure they are valid so that the Pending Service Routing record will be created without any issues.
You can avoid hard coding directly in the Flows by using Custom Labels.
2. If you are using Status-Based capacity model, don’t route the records if they are in “Values for Completed”. Always route only when they are in “Values for In-Progress”.
3. Please don’t Update the Record in a Record-Triggered Flow and route in the same transaction. I had faced this issue when the Case was updated to a Queue(with no routing configuration) and used Route Work action to route the Case in the same Record-Triggered Flow.
4. If Route Work is used in the Flow to route the records and if the Omni-Channel limits are exceeded already, then we get this exception.