If you have issue— verify you are using the Safari browser to download the macOS
you can try
macOS 10.14 Mojave - Technical Specifications:
https://support.apple.com/kb/SP777
Upgrade to macOS Mojave - Official Apple Support
https://support.apple.com/macos/mojave
https://itunes.apple.com/us/app/macos-mojave/id1398502828?mt=12
MacBook (Early 2015 or newer)
MacBook Air (Mid 2012 or newer)
MacBook Pro (Mid 2012 or newer)
Mac mini (Late 2012 or newer)
iMac (Late 2012 or newer)
iMac Pro (2017)
Mac Pro (Late 2013; Mid 2010 and Mid 2012 models with recommended Metal-capable graphics cards)