i have referred above link to block the transition of the story, if subtask status is not closed. But how to add validator message for this? because on screen it doesn't show anything and doesn't do anything. So there's no way for a user to understand that subtask needs to be closed to apply transition.
When you add a Workflow Condition, the conditions are evaluated before the transition is made available. No message will be presented in this case.
If you want a message presented, you need to add a Validator instead so that the user can try the transition and then be prevented from completing it and a message shown.
Jira Cloud does not natively have a Validator option to support this. You would have to look into adding a third party app to your instance.
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