When starting Mockplus Classic, you may get a prompt as below:
This is because Mockplus Classic is a 32-bit app, and does not offer a 64-bit version temporarily.
Starting with macOS High Sierra 10.13.4, an app that uses 32-bit processes will activate this alert, which pops up only when the app is started for the first time. You just need to click “OK”, and it will not put on any impact on your daily use.