The activity name you passed as a start activity is not correct.
The problem you are facing is related to ADB not able to find Activity which we are passing in command line.
If you are not able to launch app using simple ADB command from command line, it means your activity package name is not correct.It is even not related to appium. Its plain adb command.
I would suggest you to install app manually on to device using command -
adb install {application path}
Then install apk info from playstore. Open APK info application and get details of the package name of application. and Package name of Dashboard activity.
Then run this command from command line -
adb shell am start -n {application package name}/{Launcher activity package name}.activityName
ex : adb shell am start -n com.popcorn.copartapp/com.x.y.activitypackagename.activityName
Similar discussion is ongoing at thread - Getting Error info: [debug] Error: Activity used to start app doesn't exist or cannot be launched! Make sure it exists and is a launchable activity - #10 by RamS