SharePoint Online Rest API (Add ListItem)

I have issue with Adding List Item But I can Read List Item without any issue. I will narrate full step how I did. I want to use REST API outside SharePoint Online.

1. I register App by going to https://xxxx.sharepoint.com/_layouts/15/appregnew.aspx on SharePoint Online.
2. When I register I mention my client id, client secret, app domain and redirect uri
3. Once I did I find my site realm by navigating to https://xxxx.sharepoint.com/_vti_bin/client.svc
4. Now I navigate to https://xxxx.sharepoint.com/_layouts/15/OAuthAuthorize.aspx?client_id=my_client_id&scope=app_permissions_list&response_type=code&redirect_uri=redirect_uri
5. I pass client id and redirect uri which I mention when I register App and mention scope as List.Read List.Write, So I got code which expire after 5 minutes
6. From that code I navigate to https://accounts.accesscontrol.windows.net/site_realm/tokens/OAuth/2 where I pass in body
   • grant_type = authorization_code
   • client_id = client id @ site_realm
   • client_secrete = client secrete
   • redirect_uri = redirect url
   • resource = audience principal ID/ my sharepoint domain @ site_realm
7. And I got access token and refresh token. Where access token remain for 12 hours and after that you can do point 6 with refresh_token 

After that I run below code to get Custom List items

$.ajax({
        url: "https://xxxx.sharepoint.com/_api/lists/getbytitle('Feedback')/items?$select=Title,URL",
        method: 'GET',
        headers: {
          "Accept": "application/json; odata=verbose",
          "Authorization": "Bearer " + accessToken,
        }
      })

This works without issue, but when I try to add list item I get error Access denied. You do not have permission to perform this action or access this resource

$.ajax({
        url: "https://xxxx.sharepoint.com/_api/lists/getbytitle('Feedback')/items",
        method: "POST",
        contentType: "application/json;odata=verbose",
        data: JSON.stringify(data),
        headers: {
          "Authorization": "Bearer " + accessToken,
          "Accept": "application/json; odata=verbose",
          "Content-Type": "application/json",
        },
        success: function (data) {
          alert('Item added successfully');
        },
        error: function (error) {
          alert("Error: " + JSON.stringify(error));
        }
      })

Please help to resolve the issue of access denied and let me know what I am missing