Double check the unlocking manual.
Direct unlock for ZTE N720 - Select "Qualcomm" platform from the tab menu in the upper left side of the software
- Go to "Unlock" tab
- Connect turned ON phone to PC with USB cable
- Install required drivers (drivers will be installed from the phone automatically) only if the phone is connected for the first time
- Select USB Diagnostic Port in the ports selection tab
- Press "Unlock" button *