Not able to post on facebook timeline: getting error message "ERROR(#100)The parameter object is required"

Question

I have a website. I need to share content on facebook. I had created custom story "Participate in a Engagement" with respective action "Participate" and object "Engagement".My problem is to get explicitly_shared permission from facebook,I need to show user what is going to posted. When i am posting using FB.api like below, it is posting successfuly. Approach 1 :

<div id="fb-root"></div>
<script>
    window.fbAsyncInit = function() {
        FB.init({
          appId      : "Some App ID",
          status     : true,    
          cookie     : true,    
          xfbml      : true,     
          version    : 'v2.0',  
        });
      };
    
          // Load the SDK Asynchronously
          (function(d, s, id){
             var js, fjs = d.getElementsByTagName(s)[0];
             if (d.getElementById(id)) {return;}
             js = d.createElement(s); js.id = id;
             js.src = "//connect.facebook.net/en_US/sdk.js";
             fjs.parentNode.insertBefore(js, fjs);
           }(document, 'script', 'facebook-jssdk'));
    
        function postFBShare() {
            var fbparam= {
                            "app_id":"Some App ID",
                            "url":"Some url",
                            "title":'Some Title',
                            "image":[
                                     {url:"Some image url"}
                                     ],
                            "description":'',
                            "explicitly_shared": "true"
                        };
            FB.api(
                      'https://graph.facebook.com/me/{namespace}:participate ',
                      'post',
                      {
                        engagement: fbparam
                      },
                      function(response) {
                        // handle the response
                      }
                    );
        }
    </script>
    <input type="button" value="fb share" onclick="postFBShare();">

Approach 2: but to show user wht is going to post i need an object to post.I wrote the following code to achieve this.

function preFBAction(videoURL){
                var fbparam= {
                        "app_id":"Some App ID",
                        "type" : {namespace}:engagement,
                        "url":"Some url",
                        "title":'Some Title',
                        "image":[
                                 {url:"Some image url"}
                                 ],
                        "description":'',
                        "explicitly_shared": "true"
                    };
                FB.api(
                          '/app/objects/{namespace}:engagement',
                          'post',
                          {
                            engagement: fbparam
                          },
                          function(response) {
                            // handle the response
                             if (response && !response.error) {
                                 FB.ui(
                                        {
                                            method: 'share_open_graph',
                                            action_type: '{namespace}:participate ',
                                            action_properties: JSON.stringify({engagement:response.id})
                                        },
                                      function(response) {
                                        // handle the response
                                      }
                                    );
                             }
                          }
                        ); 
};

Approach 3: I tried with using only FB.ui,but getting following error in share dialog "Action Requires At Least One Reference: The action you're trying to publish is invalid because it does not specify any reference objects. At least one of the following properties must be specified: other." The code I tried is-

var obj={
    method: 'share_open_graph',
    action_type: '{namespace}:participate ',
    action_properties: {engagement:fbparam}     
};
 FB.ui(obj,function(response) {
    // handle the response
}); 

So if someone know how to do this and where I am going wrong, help out. Thanks!!

UPDATE

Using og tags on public page I am able to post on wall successfully and as well as in Approach 2 if I use "/me/objects/.." in place of "/app/objects.." Post gto posted on facebok but this time i got created in newz feed as well as activity log, which is not according to facebook policies.(similiar problem mentioned here.)