This guide shows how to append the severity field to a comment if the field was changed using a transition.

Precondition

In the workflow add a transition with a transition screen that has the severity field on it.

Step by step

Create an Action
Choose Jira Core as template group
Select Update comment as template
Click Create
Change the URL to {{baseUrl}}/rest/api/2/issue/{{issue.key}}/comment/{{comments.latest.id}}
Add authentication (use basic auth and a system user)

Add a body

{
    "body": "Severity has changed to {{issue.severity}} due to {{comments.latest.body}}"
}

Click on Triggers & Condition
Add Update as event
Use JQL to limit the project: project = myproj
On Field select Severity

Thats it!

This should result in that when ever a transitions is done with the Severity screen and a comment is added, then the comment should be updated to say: Severity has changed to {{issue.severity}} due to {{comments.latest.body}}

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