Sub-tasks on the User story map
Sub-tasks will be displayed on the User User story map page attached to their parent story/item.

Creating Sub-tasks on the User story map
Sub-tasks for an issue will appear underneath that issue on the User story map. You can expand/collapse the Sub-tasks view for each issue.

Sub-tasks cannot be created on the User story map if there are required fields.
Create a sub-task on the User story map using the Quick Actions menu
You can open the Quick Actions menu in 2 ways: right-click or by hovering over the issue and clicking on the … menu.
Open the Quick Actions menu
Click on Add a Sub-task
Type the Summary and hit enter to continue creating sub-tasks beneath your chosen issue
Create a sub-task on the User story map using the + icon
You can create additional sub-tasks on an issue with existing sub-tasks by click on the + icon
Click on the + icon in the Sub-tasks expand/collapse bar
Type the Summary and hit enter to continue creating sub-tasks beneath your chosen issue
