how to go to call method inside asp page from js file

<button onclick="javascript: UploadPainImage();return false;">Save Edited Image</button>

function UploadPainImage() {
  
    // generate the image data for PainIamge 
   
    var Picpain = document.getElementById("myCanvas1").toDataURL("image/png");
    Picpain = Picpain.replace(/^data:image\/(png|jpg);base64,/, "")
//   
    
    // Sending the image data to Server
    $.ajax({
        type: 'POST',
        url: 'SaveRomInspectionImg.aspx/UploadPainImage',

        data: '{ "imageData1" : "' + Picpain + '" }',
        contentType: 'application/json; charset=utf-8',
        dataType: 'json',
        success: function (msg) {
            alert("Done,Pain Image Uploaded .");
        }
    });
}

using System;
using System.Web;
using System.IO;
using System.Web.Script.Services;
using System.Web.Services;
using System.Data.SqlClient;
using System.Data;
using System.Configuration;

[ScriptService]
public partial class Doctor_SaveRomInspectionImg : System.Web.UI.Page
{
    //public static string patientid;
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    [WebMethod()]
    public static void UploadPainImage(string imageData1)
    {
        string Pic_Path = HttpContext.Current.Server.MapPath("RomInspectionImg.png");
         using (FileStream fs = new FileStream(Pic_Path, FileMode.Create))
        {
            using (BinaryWriter bw = new BinaryWriter(fs))
            {
                byte[] data = Convert.FromBase64String(imageData1);
                SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["con"].ConnectionString);
                SqlCommand cmd = new SqlCommand();
                cmd.CommandText = "sp_updateRomInspectimage";
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.Add(new SqlParameter("@pid", GlobalVariable.patid));
                cmd.Parameters.Add(new SqlParameter("@painimg", data));
                cmd.Connection = con;
                con.Open();
                cmd.ExecuteNonQuery();
                con.Close();
                bw.Write(data);
                bw.Close();
            }
        }
    }
    
}