The Unique Key property in the Orchestrator Queue configuration allows you to specify whether the queue items should have unique references or not. A reference is a string value that can be used to identify a queue item. If the Unique Key property is set to Yes, then Orchestrator checks if the reference of the new queue item already exists in the queue, and rejects the item if it does. This way, you can prevent adding duplicate items to the queue and ensure that each invoice is processed only once. If the Unique Key property is set to No, then Orchestrator does not perform this check and allows adding items with the same reference to the queue. This option can be useful if you want to process the same invoice multiple times for different purposes or scenarios. References: Managing Queues in Orchestrator - UiPath Documentation Portal, Managing Queues in Orchestrator - UiPath Documentation Portal, Orchestrator Queue - “unique reference” is enforced - Help - UiPath Community Forum