Summary

Unable to create subtasks on Project 'Issues' screen. 

Environment

Jira Cloud

Diagnosis

On the 'Issue View' screen when selecting 'Create Subtask', after filling out the form user is presented an error stating: "We couldn't create the subtask. The default assignee does NOT have ASSIGNABLE permission OR Unassigned issues are turned off."

Cause

This is potentially do to a permissions issue on the Project. You can verify this in the browser devtools, should you see a HTTP 400 response code with a header response similar to:

{"errorMessages":[],"errors":{"assignee":"The default assignee does NOT have ASSIGNABLE permission OR Unassigned issues are turned off."}}

Solution

Should you see this response, as an administrator, check the project settings:

1. On the sidebar, tap 'Project Settings' and check the 'Details' tab
2. There, ensure that 'Project Lead' and 'Default Assignee' fields have valid entries.

If the 'Default Assignee' is not a valid assignable user, the sub-task will not be able to be created. In this case, update the project settings to either 'Unassigned' or to a valid user and then 'Save'. This should address to error and allow you to create Subtasks as normal.