I am trying to make an audio visualizer, but when i try to load it at some point, the php is considered as an not allowed method

POST http://127.0.0.1:5500/php/index.php 405 (Method Not Allowed)

Here is the point where its having the error:

async function uploadFile() {
  if (realFileBtn.value) {
    customTxt.innerHTML = realFileBtn.value.match(
      /[\/\\]([\w\d\s\.\-\(\)]+)$/
    )[1];
  } else {
    customTxt.innerHTML = "No file chosen, yet.";
  }
  let formData = new FormData();           
  formData.append("file", fileupload.files[0]);
  await fetch('php/index.php', {
    method: "POST", 
    body: formData
  });    
  alert('The file has been uploaded successfully.');
}