2 - What OS is the app compatible with?

Answer:

It works well in any Android version.

List of supported devices

Notes: please frequently visit the section of announcements on the support site for the latest updates.

Just less than 5 minutes to configure all.
You can just try to visit the below links for 'how to install the app on an Android device' and search 'essential settings' for more details.

Could you please tell me if you have access to the target device

Physical access of 5-10 minutes is required for the installation. After the installation is completed, all the data monitored will be available through your online account immediately. You can check it at your control panel site at the bottom of this email.

Monitoring the non-default applications such as WhatsApp, Facebook, Viber, Skype, Line ... can be activated on the Android-based target phone if it is ROOTED. It also allows you to take advantage of many proper options in your cPanel ("Get GPS Now," "Sync Now"). The rooting procedure is unique for each phone model/OS version. It is possible to use the target app on non-rooted devices as well.

If you want to root your device, you can search on the forum site to see many posts.