Mac error - "Can't open. Unidentified developer"

We don't sell through the Apple store. They will only approve products they make money on and so they play that game which is a huge disservice to the end users. 

Here is what Apple's site says

In recent macOS when an app fails to install because it hasn't been notarized or is from an unidentified developer, it will appear in System Preferences > Security & Privacy, under the General tab. Click Open Anyway to confirm your intent to open or install the app.