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Unfortunately, JIRA does not have the functionality to automatically create a story when an Epic is transitioned, however, you can achieve it using some plugins.
My recommendation is to use Automation for JIRA and configure a rule like this:
Please, let me know if this is the feature you are looking for.
Hi All! We’re excited to share the launch of an announcement banner that lets Jira site administrators communicate directly to their users across their Jira Cloud instance. ...
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