...
For more information on how to add a post function to a workflow in Jira, see the Jira documentation.
Precondition
...
There are several ways in which preconditions If you are using preconditions with a JSU post function, they can be evaluated in the context of a post functionone of the following ways:
Ignore precondition: (By default every precondition is ignored which means that the post function will always be performed)
True: (Precondition must be true to execute a post function)
False: (Precondition must be false to execute a post function)
...
Learn more about JSU preconditions in Workflow Preconditions.
Issue relation
The field can be on the issue in transition(within the same issue) or on a related issue, like a subtask, a linked issue, or an issue within an Epic (during the transition on the Epic).
...
The ‘Create' transition is the first transition, which does not have a source status (only destination status - usually Open). Instead of using the ‘Clear Field Value’ post function in the ‘Create’ transition, you might configure no default value for that custom field and don't show it on the Create screen. If you are using the ‘Clear Field Value’ post function in the 'Create’ transition, you must put it before the "Creates the issue originally" post function except when clearing labels, which need to be cleared after the issue has been created.
...
Put the ‘Clear Field Value’ post function anywhere before the "Update change history for an issue and store the issue in the database" post function.
Example
A workflow is configured so the 'Close' transition has the 'Clear Field Value' post function. The function is configured to clear the 'Security Level' field. If a user closes an issue on this workflow, the value of the 'Security Level' field will be cleared.
...