Message has already been processed

This error occurs because the request sent to Unifi references a message ID that corresponds to an existing transaction in the receiving Unifi system. This usually happens when the receiving Unifi systems integration has been linked to two separate systems, i.e. a dev and UAT system, and therefore your message IDs are duplicated.

Ensure that the message IDs you are sending are unique, and/or you remove the preciously duplicated transactions in the receiving system.