Can't sign up for new service online?

I am trying to my family from AT&T to T-Mobile (5 lines). I went on to t-mobile.com and selected a plan, selected the phones (2 new iPhones and 3 transfers of existing phones.) Everytime I try and check out I get an error.

Is there an issue with the Website, or does t-mobile's website just suck? I really didn't want to have to go to a store to do this.