If you have GoSMS installed on your Android phone, and messages aren't forwarding to the MightyText Web App:
1 - Launch GoSMS app on your Android phone
2 - Under 'Menu -> Settings -> Receive Settings' - uncheck the box that says 'Disable other message notification'
3 - Now, see if incoming messages are properly getting forwarded to the MightyText Chrome Extension
4 - If it doesn't work, restart your phone and see if incoming messages now get forwarded to the MightyText Chrome Extension
5 - If it still does not work, you should un-install GoSMSPro and see if that fixes the problem.