I have created a global apex class by declining "implements Loop.IApexDataSource" to the class. But i can't able to see the the apex class under the in Apex class options under Apex Data in my pac. i am system admin and i have access to the apex class in my profile settings. 

Along with that when i click the apex data on the package i am facing the following error message.

"Error: An unexpected error has occurred. Please contact Nintex Support if this error persists."