So the hosting is in their Grassroots.org Toolbox. They should set it up themselves but there is a problem with the API so they may not have done it correctly. Please ask them to login to Grassroots.org (or give you the login information) and submit the hosting application within the toolbox.

Once submitted, however, you will need to reference http://help.grassroots.org/hosting-fix for a quick way to finish the set-up process. You will then be able to FTP the site with the domain name and password.

Please let me know if you have any further problems. Thanks!