Post image to private server

[alpha_coder]

Hi,
I want to post image to my private server through arcgis appstudio using javascript, but it receive corrupt image, This is my code below. Even when i console base64 image and convert it through online base64 to image convertor tool, it gives corrupt image something.. what should i do

import QtQuick 2.13
import QtQuick.Layouts 1.13
import QtQuick.Controls 2.13
import ArcGIS.AppFramework 1.0
import Esri.ArcGISRuntime 100.6
import QtQuick.Dialogs 1.0
import Qt.labs.settings 1.0
import QtQuick.Controls.Material 2.1
import "../../controls" as Controls
import "../../assets/js/backend.js" as Backend

App {
    id: appdem
    width: 400
    height: 640

    ColumnLayout {
        anchors {
            fill: parent
            margins: 10
        }

        ImageObject {
            id: imageObject

            onUrlChanged: {
                console.log("url:", url);
            }

            onImageChanged: {
                var buffer_data = imageObject.toArrayBuffer();
                Backend.demo(buffer_data);

            }
        }
        Button {
            text: "Load"
            onClicked: {
                console.log("API Key::"+settings.api_key);
                var img_path = "/Desktop/Modern-Office-3-Skype-Backgrounds.jpeg";
                imageObject.load(img_path);
            }
        }

        Image {
            fillMode: Image.PreserveAspectFit
            source: imageObject.url
            horizontalAlignment: Image.AlignHCenter
            verticalAlignment: Image.AlignVCenter
            cache: false
        }
    }

}

Backeend file code

function arrayBufferToBase64( buffer ) {
    var binary = '';
    var bytes = new Uint8Array( buffer );
    var len = bytes.byteLength;
    for (var i = 0; i < len; i++) {
        binary += String.fromCharCode( bytes[ i ] );
    }
    return Qt.btoa( binary );
}

function demo(img_binary){
    var endpoint = 'insertDamageReport';
   var base64String = arrayBufferToBase64( img_binary );
   console.log(base64String);
    //create HTTP REQUEST Object
   var xmlhttp = new XMLHttpRequest();
    //Opend request
    xmlhttp.open('POST', "https://abc.co.nz/wp-json/hhq/v1/"+endpoint, false);
    ///Set header data
    xmlhttp.setRequestHeader("Content-Type","application/json");
    xmlhttp.setRequestHeader("X-Requested-With", "XMLHttpRequest");
xmlhttp.setRequestHeader("AuthenticationInfo",JSON.stringify({"_key":"","_secret":"","device_id":"","access_token":""}) );
    //Set request to server
    var data = {"booking_id":1,"report_content":"test","images":base64String};
    let params = (typeof data != 'undefined')?JSON.stringify(data):''
    xmlhttp.send(params);
    ///Handle Response
    if (xmlhttp.readyState === 4 && xmlhttp.status === 200) {
        console.log(xmlhttp.responseText)
    }else if(xmlhttp.readyState === 4){
        console.log(xmlhttp.responseText);
    }
}