Hello Tausif,
It looks like the import is not working because it is mapping a field, probably your story description field or title field on the field storypoints.
This can be due to a wrong excel format(on your side) or by a wrong mapping on the side of the website(mendix).
Did you use this template and did you not delete any columns:
If you did so then file a ticket if not try it with the template
Hope this helps,
Good luck!