Hustle looks really cool! I am trying to set up my first opt-in using MailChimp, I double checked my API key and it won't bring up any of the MC lists available in the Wizard in Hustle (the loading graphic just keeps spinning). I am currently using both WPMUDev's Slide In and Gravity Forms with MC so I know the API key works. One thing I saw in MC is: (211) List_InvalidOption - this is at the same date/time(s) that I am trying to setup Hustle.