How do I add tasks on the WBS Gantt Chart?

[松宮 小雪]

On the WBS Gantt Chart, click "Add" -> "Tasks.
The "Key" field of the added task will display "*TEMP-XX".
After saving, the following message will appear.

「Error: Epic link cannot be created. Please check Issue Create Screen settings.」

I do not know the cause of this.
I also do not know where the Issue Create Screen setting is located.

Please share your wisdom.
I am Japanese, so I apologize if my English is difficult to understand.