Please try restarting your Mac.

In case the issue remains, please check your Mac security settings.

You can click Apple icon on the top left of the desktop and select System Preferences and select Security&Privacy .

Click the lock icon at the bottom of the General tab and enter your password.

For MacOS Yosemite and earlier, you can select 'Allow apps downloaded from - Anywhere'.

For the later MacOS versions please select 'Allow apps downloaded from - Appstore and verified developers '.