While you do not have any billing information, the X.IO site will display a red bar at the top of the page and, you will not be able to add applications to your account. Click on the link, in the red bar, and you will be taken to a page where you can update your billing information.
Fill out the fields with the appropriate information and click the update button. Once that is complete, the red bar at the top of the page will disappear and, you will be able to add applications to your account!
Continue to Step 3 for instructions on adding applications to your account.