Sveltekit : custom express server causing not found errors during fetch

Question

I'm trying to use sveltekit with a custom express server as outlined in the sveltekit doc here

Here is my server :

import { handler } from '../build/handler.js'
import express from 'express';

const app = express();


app.use((req, res, next) => {
    const corsWhitelist = [
        "http://localhost:5000",  // front section
        "http://localhost:4000", //menumanagement section
        "http://localhost:2000", //owner section
        "http://localhost:2500", // orders dashboard section
        "http://localhost:5173", //sveltekit apps
        
    ];
    if (corsWhitelist.indexOf(req.headers.origin) !== -1) {
           res.header('Access-Control-Allow-Origin', req.headers.origin);
           res.header("Access-Control-Allow-Headers", "Origin, X-PINGOTHER , X-Requested-With, Content-Type, Accept");
           res.header({'Access-Control-Allow-Credentials': true});   
           res.header('Access-Control-Allow-Methods','GET,PUT,POST,DELETE,OPTIONS');
    }

    next();
}); //end app use for muliple origins

// add a route that lives separately from the SvelteKit app
app.get('/healthcheck', (req, res) => {

    console.log("healthcheck inside expxress server")
    res.end('healthcheckok');
});

// let SvelteKit handle everything else, including serving prerendered pages and static assets
app.use(handler);

app.get('/expresskit', (req, res)=>{
    console.log("expresskit handle ....")
    res.end("expresskit")
})

app.listen(3000, () => {
    console.log('custom server is listening on port 3000');
});

created a sveltekit and in the index page - in the +page.svelte I created a button

<button on:click={getexpresskit}>get expresskit</button>

in the script I run the function :

 async function getexpresskit(){

      let response = await fetch('http://localhost:3000/expresskit')
      let serverdata =await response.json()
      console.log("-------------", serverdata)
      } //end getexpresskit

I get this in the console : I get 404 /expresskit not found

 Error: Not found: /expresskit
    at resolve (file:///D:/mycode/sveltekit/joyofcodesocket/socketjoyofcode/build/server/index.js:3915:18)
    at resolve (file:///D:/mycode/sveltekit/joyofcodesocket/socketjoyofcode/build/server/index.js:3749:34)
    at #options.hooks.handle (file:///D:/mycode/sveltekit/joyofcodesocket/socketjoyofcode/build/server/index.js:3981:61)
    at respond (file:///D:/mycode/sveltekit/joyofcodesocket/socketjoyofcode/build/server/index.js:3747:43)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)

I tried to rebuild the kit folder again, so I ran npm run build in my kit folder, get the following error :

node:internal/event_target:1012
  process.nextTick(() => { throw err; });
                           ^
Error: 405 /
To suppress or handle this error, implement `handleHttpError` in https://kit.svelte.dev/docs/configuration#prerender
    at file:///D:/mycode/sveltekit/joyofcodesocket/socketjoyofcode/node_modules/@sveltejs/kit/src/core/config/options.js:212:13
    at file:///D:/mycode/sveltekit/joyofcodesocket/socketjoyofcode/node_modules/@sveltejs/kit/src/core/postbuild/prerender.js:64:25
    at save (file:///D:/mycode/sveltekit/joyofcodesocket/socketjoyofcode/node_modules/@sveltejs/kit/src/core/postbuild/prerender.js:403:4)
    at visit (file:///D:/mycode/sveltekit/joyofcodesocket/socketjoyofcode/node_modules/@sveltejs/kit/src/core/postbuild/prerender.js:236:3)
Emitted 'error' event on Worker instance at:
    at [kOnErrorMessage] (node:internal/worker:300:10)    at [kOnMessage] (node:internal/worker:311:37)
    at MessagePort.<anonymous> (node:internal/worker:212:57)
    at [nodejs.internal.kHybridDispatch] (node:internal/event_target:737:20)
    at exports.emitMessage (node:internal/per_context/messageport:23:28)

Node.js v18.16.1

I'm aware that the error pointing to build/index.js instead of my server but I don't know how to fix it. Where do I correct the build script to point to my custom express server? How do I fix it?

Is there a resource with a detailed step by step on how to create and use custom express server instead of asking the same question here>?