You can apply for it from the button [登録変更 "change registration"] at the section of "Seikyu gaku Oshirase email (billing amount notification email)" on the top screen of "We...
Please log in to "Web Billing" and press the button [Webビリング対象回線追加変更 (add and change the lines for Web Billing)] on the left of the screen.
When you add lines, m...