How to pass the texbox value in webmethod in codebehind through ajax?

Try like this:

$(function () {
	var stDt = $("#<%= txtStartDt.ClientID %>").val();
	var endDt = $("#<%= txtEndDt.ClientID %>").val();

	$.ajax({
		type: "POST",
		url: "InteractiveDashboard.aspx/Web_GetTotalSaleslist",
		data: JSON.stringify({ StartDate: stDt, EndDate: endDt }),
		contentType: "application/json; charset=utf-8",
		dataType: "json",
		success: function (response) {
			alert("Success: " + response.d);
		},
		failure: function (response) {
			alert("Error: " + response.d);
		},
		error: function (response) {
			alert("Error: " + response.responseText);
		}
	});
});

you can follow the below steps:

Create a Web Method in Code-Behind:

• In your code-behind file (e.g., YourPage.aspx.cs for Web Forms or a controller for MVC), create a static method and decorate it with the [WebMethod] attribute.

using System.Web.Services;

public partial class YourPage : System.Web.UI.Page
{
    [WebMethod]
    public static string YourWebMethod(string textboxValue)
    {
        // Your logic here
        return "Received value: " + textboxValue;
    }
}

Call the Web Method using AJAX:

• In your webpage (HTML or ASPX file), use JavaScript/jQuery to capture the textbox value and make an AJAX call to the web method.

Call Web Method

Retrieve and Process the Value in the Web Method:

• In your web method, receive the textbox value as a parameter and process it as needed

[WebMethod]
public static string YourWebMethod(string textboxValue)
{
    // Process the textbox value
    return "Received value: " + textboxValue;
}

This way, when the "Call Web Method" button is clicked, the textbox value will be sent to the web method through an AJAX call, and the response from the web method will be displayed in an alert box