Get recommendation from LinkedIn API returns blank card [:] as response

I have created a web application from which I am trying to get user recommendations from his / her LinkedIn profile using url

String url = " https://api.linkedin.com/v1/people/~:(recommendations-received:(id,recommendation-type,recommendation-text,recommender))?format=json "

When I use this url in Api Explorer it works fine. And gives the result: -

{   "recommendationsReceived":  {
    "_total": 2,
    "values":  [
       {
        "id": 558598601,
        "recommendationText": "xxx is among the best team players I ever worked with.  He has handled client effectively with smooth operations. I had always seen him as person with solution mindset and always look for  solution rather than thinking about the problem. ",
        "recommendationType":  {
          "code": "colleague"
        },
        "recommender":  {
          "firstName": "XXX",
          "id": "YYYY",
          "lastName": "XXX"
        }
      },
       {
        "id": ZZZZ,
        "recommendationText": "XXX is one of the most dedicated person at work.I always him with a flexible attitude and ready to adapt himself in all situation.I have seen him work all night to catch up all the deadlines and deliver on time ."
        "recommendationType":  {
          "code": "colleague"
        },
        "recommender":  {
          "firstName": "XXX",
          "id": "YYYY",
          "lastName": "XXXX"
        }
      }
    ]   } }

      

        
        
        
      

    

The problem occurs when I use this url in my developer app. This gives no error to just return an empty map [:] as output in the response

Regardless of these recommendation fields, I am successfully getting basic user profile data like email, id, image, firstName, lastName.Means my code works for other fields but not for these recommendation fields *

To find a solution I did some internet surfing and found the Linked API docs link

Related API docs

Per the Docs, once selected, profile fields are only available to apps that have been applied and approved for use with the LinkedIn Program: Recommendation Fields

I already created a LinkedIn developer account to get the key and secret So how can I apply and get permission to apply on LinkedIn links. I've already seen LinkedIn support but can't find a way to ask a question in the LinkedIn Help System

Please suggest me the right way.