When a sub-task is created, its summary, issue key and date, and time of creation will be added to the description of the parent issue.
Select Parent of current issue.
The parent of the current issue will be updated.
Select Description.
In the popup field:
Set the Value* to Set field value manually (parser expression) and insert the following expression:
%{parent.description} Sub-task %{issue.key} has been created on %{system.currentDateTime}.
The issue key and date and time of creation of the sub-task will be added to the description of the parent issue.
Choose which user* will be able to execute the post function. By default, it is set to the Current user.
Insert the following expression:
%{issue.issueType} = "Sub-task"
The post function will only be executed if the created issue is a sub-task.