PluginClassLoader - ClassNotFoundException after moving class to another package.

Assume my package name is com.name.app

I have a class ApiHelper which has a ResponseHandler interface. Another class, ButtonActionHandler (extends AnAction) implements ResponseHandler from ApiHelper.

Everything works fine at this point. But if I move ApiHelper to com.name.app.helpers package I get NoClassDefFoundError &  PluginClassLoader - ClassNotFoundException.

Any idea why this is happening after moving file to another package?