We're so sorry for the inconvenience here! This can happen in a few instances:
1. You may already have an account associated with that phone number.
2. You may be trying to use a VoIP number, which we currently don't support.
3. There may be a technical issue preventing us from verifying your phone number.
In each of these cases, please reach out to us at http://contact.ritual.co/ and provide the email address and phone number that you would like to sign up with, and we'll happily help you to set up your account!