If you are running Sierra (actually version 10.12.3) on your Mac the GateKeeper of the OS prevent you from installing software
not from the Apple Store and/or not signed by a known Apple developer. That is done to keep your Mac clean from malware and other buggy software
is not signed with a valid developer certificate.
You may have a chance to install it anyhow when you go after seeing the refuse message to the Mac system settings and there to Security
. There you might see a button allowing you to install nevertheless to you own risk.