For MightyText to properly communicate with your phone, it needs to be able to connect to your phone over the internet. If you are using WiFi and your phone goes into sleep mode, then MightyText may mot be able to communicate with your phone unless the Wi-Fi sleep settings are set correctly. Steps below.
On your Android phone:
For Android 2.3 and earlier
1) Navigate to Menu > Settings > Wireless & Networks > Wi-Fi settings> and select the menu button again.
2) You’ll be prompted to either scan or select advanced. Select “Advanced”
3) Select “Wifi sleep policy” , and you will have a couple of options to select from. Choose “Never”.
For Android 4.0 (Ice Cream Sandwich) and later:
1) Navigate to Menu > Settings > WiFi and select the menu button again.
2) Select Options, Advanced
3) Set “Keep WiFi on during sleep” to “Always”