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Use case
When an issue is created, sub-tasks for each option selected in the 'Checkbox' custom field are added.
Issue Event
Create a new rule and name it appropriately.
Providing a description will help you to identify what the rule does but this step is optional.
Add a trigger and choose the Issue event → Issue created
No further configuration needed. The automation rule is triggered every time an issue is being transitioned.
Create Issue
Add Action → Create Issue
Issues to be created*
Choose Multiple issues
Parser Expression*
toStringList(%{trigger.issue.cfnnnnn})
with the Parsing mode set to String List
Note that: nnnnn is field code for the checkbox custom field.
Issue type*: Choose Sub-task
Parent issue*:
Choose Trigger issue
Summary*
Use the following parser expression :
^ %
with the Parsing mode set to Advanced