So I'm trying to use MathPix API to get pure Latex from processed image in my Django project.

I use few <input type="file"> fields and event listener on each one. After change event the file is validated (if it is a .jpg, .png etc). Next I use URL.createObjectURL() function to create a url for uploaded file without saving it before to db.

function checkExtension(event) {
    var input = event.srcElement;
    var fileName = input.files[0].name;
    var extension = fileName.substr(fileName.lastIndexOf("."));
    var allowedExtensionsRegx = /(\.jpg|\.jpeg|\.png|\.gif)$/i;
    var file = document.getElementById(event.target.name)
    if (allowedExtensionsRegx.test(extension) == true) {
      file.setAttribute("class", "btn-success p-2 rounded")
      const image = input.files[0];
      const image_url = URL.createObjectURL(image)
      snip_request(image_url)
    }
    else {
      file.setAttribute("class", "btn-danger p-2 rounded")
    }
}


function snip_request(image_url){
  if(image_url) {
    const appId = "XXXXXXXXXXXXXXXXX";
    const appKey = "YYYYYYYYYYYYYYYY";
    var url = "https://api.mathpix.com/v3/latex";
    var _data = {
      "src": image_url,
      "formats": "text",
      "data_options": {
        "include_asciimath": true,
        "include_latex": true
      }
    }
    var _header = {
      "content-type": "application/json",
      "app_id": appId,
      "app_key": appKey
    }

    const response = fetch(url, {
    method: "POST",
    body: JSON.stringify(_data),
    headers: _header
  })
  .then(response => response.json())
  .then(json => console.log(json));;

  }
}

Unfortunately at the end of the day I get error message:

{
    "error": "blob:http://localhost:8000/4c523864-93ec-452a-ace1-0156b63e9837: TypeError: Only HTTP(S) protocols are supported",
    "error_info": {
        "id": "image_download_error",
        "message": "TypeError: Only HTTP(S) protocols are supported",
        "url": "blob:http://localhost:8000/4c523864-93ec-452a-ace1-0156b63e9837"
    }
}

I have no clue why this is not working? Is it the problem with the "temporary URL" or the way of file being downloaded by the server? I'm pretty new in Java Script so any advice will be appreciated.