After trying for the past 24 hours to make this work, I finally got connected this afternoon. I contacted support to try and track down if it was any of the issues reported here. The first rep I got was useless - didn't even understand what I meant when I said the button was greyed out. The second though was quite helpful. She discovered the account needed updated credit information. She processed that but it still didn't work. A third rep a few hours later recommended I try resetting my network settings on my phone (Tap Settings > General > Reset > Reset Network Settings). Once I did that I could finally click the button and never ran into any of the other error codes people are referencing here.
TL,DR:
1. Credit information needed to be updated through rep.
2. Had to reset network settings once that was done.
