Why does it say “You need to check and update your contact information.” at the top of the Btwentyfour Dashboard?

If any mandatory information are missing under "MY ORGANISATION" - "My Party" you will be informed about that with a notification at the top of the Btwentyfour Dashboard.

Click the "Update your information" button to the far right of this notification to go to "MY ORGANISATION" - "My Party" where you can update your information.