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.