What is the API call to create external sharelink for a pdf

What is the API call to create external sharelink for a pdf

Here's my code

  2.         mp = Map();
  3. mp.put("Accept","application/vnd.api+json");
  4. // Parameters Map
  5. externalLinkMap = Map();
  6. externalLinkMap.put("resource_id",resource_id);
  7. externalLinkMap.put("link_name","link");
  8. externalLinkMap.put("request_user_data",false);
  9. externalLinkMap.put("allow_download",true);
  10. // Give view-only access
  11. externalLinkMap.put("role_id","34");
  12. attributesMap = {"attributes":externalLinkMap,"type":"links"};
  13. dataMap = Map();
  14. dataMap.put("data",attributesMap);
  15. // Create external share link
  16. external_link_data = invokeurl
  17. [
  18. url :"https://www.zohoapis.com/workdrive/api/v1/links"
  19. type :POST
  20. parameters:dataMap.toString()
  21. headers:mp
  22. connection:"workdrive_all"
  23. ];
The connection has the correct scope(s).

The error message is 
  1. {"errors":[{"id":"R008","title":"Unauthorized access"}]}
I know the code works for native Zoho document types such as a sheet.