We receive automated alerting emails from different monitoring sources. All emails contain an incident ID. I use automation to store this incident ID in the custom field ExternalID.
Whenever the monitoring has an update on the issue we receive another email where the incident ID is the same (same incident), but the status <> new.
How to link these issue's together based on the external incident ID?
Did several attempts, but none of them succeed. The current flow I have extracts the externalID and puts this in the custom field:

This ends with the following error:"Can't branch rule as it requires issues to have been previously created by this rule. More than likely you have not yet created an issue or the issue(s) were created in an another 'If' block or branch - these would then not be visible outside of that block/branch."
But I'm sure more issue's exist with the same external ID.
Hope somebody has the golden hint...
Jeroen