WordPress as UUID4 Validator

guid.php

<?php
include_once $_SERVER['DOCUMENT_ROOT'] . '/wp-config.php';

$select = file_get_contents('php://input');

if(empty($select)) {
    echo wp_generate_uuid4();
}else{
  wp_is_uuid( $select, 4 );
  echo 'UUID is correct';
}

index.js

function GUID_get() {
  fetch("guid.php")
  .then((res) => {
   return res.text();
  })
  .then((data) => {
  sessionStorage.setItem("UUID", data);
  console.log('UUID generated succesfull')
  })};
function GUID() {
fetch("guid.php", {
method: "POST",
body: sessionStorage.getItem('UUID')
})
.then((res) => {
 return res.text();
})
.then((data) => {
console.log(data)
})};