code: @Override
      public String[] getRequestableScopes(long clientId) throws AuthleteApiException
      {
          // Call the API.
          RequestableScopes response = executeApiCall(
                  new ServiceGetApiCaller<RequestableScopes>(
                          RequestableScopes.class, REQUESTABLE_SCOPES_GET_API_PATH, clientId));
  
          if (response != null)
          {
              // Extract 'requestableScopes' from the response.
              return response.getRequestableScopes();
          }
          else
          {
              return null;
          }
      }
docs: Call <code>/api/client/extension/requestable_scopes/get/<i>{clientId}</i></code> API.