Issue Summary

When attempting to create subtasks, clicking the create button results in no action and no error message is shown on the user interface. However, the browser's developer tools reveal a failed request with a 400 error: "The default assignee does NOT have ASSIGNABLE permission OR Unassigned issues are turned off". This error arises when the project's default assignee lacks the "Assignable User" permission in the project permission scheme, or when the "unassigned issues" setting is disabled.

Steps to Reproduce

1. Ensure the project's default assignee does not have the "Assignable User" permission, or if the default assignee is "Unassigned", disable the "Allow unassigned issues" setting in the system settings.
2. Navigate to any work item within the project and attempt to create a subtask.

Expected Results

An error message should be displayed on the UI indicating the issue as indicated in this KB article.

Actual Results

No error message is displayed on the UI, and subtask creation fails silently.

Workaround

First, verify the error using the browser's developer tools. To resolve this issue:

• If there is a default assignee in your project, ensure they have the "Assignable User" permission.
• If you are using unassigned issues, go to Jira Settings > System > General Configuration and set the "Allow unassigned issues" option to ON.