This is a bug in the Hangouts app.

If Hangouts is the default SMS messaging app on your phone in the Android Settings and outgoing messages you send from MightyText are not appearing in your Hangouts threads, please do the following.

  1. Send a message from MightyText.
  2. Using the BACK KEY on your phone, close the Hangouts app.
  3. Re-open Hangouts on your phone.
  4. Go to the thread associated with the message you had just sent using MightyText.

If the message you had sent from MightyText appears in Hangouts after doing the above steps, this is an issue with the Hangouts app on your phone.  The Hangouts app doesn't automatically check for new messages in the same session and should update to reflect the latest updates when the app is closed and opened.