[Solved] Send and parse JSON string as PostBack argument in __doPostBack method in ASP.Net

You don't need to use JSON.stringify method, as already it is JSON string.

On Server side, you need to deserialize the JSON to a class object in order to extract RecId.

Check this example.

HTML

<div onclick = "doPostBack()">
Click Me
</div>
<asp:LinkButton Text="" runat="server" />
<script type = "text/javascript">
    function doPostBack() {
        __doPostBack('DivClicked', "{ recId: 1, isSentClicked: true }");
    }
</script>

Code

public class JSON
{
    public int RecId { get; set; }
    public bool IsSentClicked { get; set; }
}
protected void Page_Load(object sender, EventArgs e)
{
    if (Page.IsPostBack)
    {
        JSON json = (new System.Web.Script.Serialization.JavaScriptSerializer()).Deserialize<JSON>(Request["__EVENTARGUMENT"]);
        Response.Redirect("DisplayMessage.aspx?senderId=" + json.RecId);
    }
}