Many software licenses allow installation on only one or two devices. If you have upgraded your computer or are trying to install it on a third machine, the key may be rejected.
Ensure your computer is connected to the internet. The software needs to ping the developer’s server to verify that the key is genuine. Why Your eStroke License Key Might Not Work estroke license key work
Sometimes, security software or firewall settings prevent the software from "calling home" to verify the key. Many software licenses allow installation on only one