Not sure if this works for everyone, but it worked for me. I had tried adding the device multiple times with multiple **5 xxxx numbers, with voice response saying it was sent to the server, but it always timed out. The echo test had worked ok.
I then noticed that Obi had sent me an email, and when I clicked on the link in the email, I was taken to a webpage where the device was added. So maybe clicking on the email link after sending a number to the server is a solution. Your results may vary. Good luck.