To install AppSync for OS 3.1.2 need to first add this repo http://apt.macosmovil.com
Here, are the steps to add macosmovil repo:
Launch Cydia, Select Manage.
Now tap the Edit button.
Now you will see the Add button, tap on it…
Now you will be prompted for the url address.
Just type apt.macosmovil.com and tap on Add Source button and let it load.
Once it is added tap on Done button.
Now you will macOSmovil repo added on top, just tap on it, you will see list of apps, just scroll down and install AppSync for OS 3.1.2.
Reboot your phone once done