How do I get JSON data from a custom entity I would like to GET JSON data from drupal 8 custom entity.
I am using ubuntu 14.04 and vagrant.
For that i have done these steps.

I have taken reference to Create drupal 8 custom entity from this link.

Enable this modules:


HAL - Core module 
HTTP Basic Authentication -Core module 
RESTful Web Services - Core module 
Serialization  - Core module 
Restui - Contributed module


RESTui Configuration:


redirect to admin/config/services/rest
Enable content_entity_example_contact entity
GET Settings done for custom entity


Save.


Permissions given for Rest full web services


Postman Plugin is integrated in to chrome.
below settings is done for postman.


Above steps i have done to GET JSON from custom entity but getting error in postman. Any suggestion or starting point will help for me.

Interestingly when i perform similar steps for drupal 8 node entity i am able to GET JSON data.



Thanks
Dou you have an access control handler or an admin permission to control view/create/update/delete access to your entities?

You need to have that, in addition to the rest specific permissions. In fact, those will go away in 8.2, only the generic entity access will matter then.