If your phone is running Android 5.0 or higher, you will also need to install our SMS app, SimplyText, and set it to be the default SMS app on your phone in order for mark-as-read to work properly.
Note: MightyText requires SimplyText to be the default SMS app on your phone for this to work because only the default app has permission to make changes to the SMS database on the phone in Android 5.0 and above. (This is a restriction on the Android platform).