Where is the error in the code when writing to a variable?

Question

PHP

Hello,

where is the mistake?

i'm trying to do this

if($_POST['generate_xml']) {

$arSelect = Array("ID", "IBLOCK_ID", "NAME", "DATE_ACTIVE_FROM",);
$arFilter = Array("IBLOCK_ID"=>11, "ACTIVE_DATE"=>"Y", "ACTIVE"=>"Y");
$res = CIBlockElement::GetList(Array(), $arFilter, false, Array("nPageSize"=>50), $arSelect);

  $site = 'http://';
  $data = date('Y-m-d');
  $dir = $_SERVER['DOCUMENT_ROOT'].'/scheme/geoObjects2.geojson';

  $data_for_write ='
  {
    "type": "FeatureCollection",
    "metadata": {
      "name": "Карта торгового центра",
      "creator": "SWP",
      "description": ""
    },
  '.
    while($ob = $res->GetNextElement()){
      $arFields = $ob->GetFields();
      $arProps = $ob->GetProperties();
  .'
      "features": [{
        "type": "Feature",
        "id": "'.echo $arFields['ID'].'",
        "geometry": {
          "type": "Polygon",
          "coordinates": "'.echo $arProps['PROPERTIES']['COORDINATES']['VALUE'].'"
        },
        "properties": {
          "description": "'.echo $arFields['NAME'].'",
          "fill": "#ff931e",
          "fill-opacity": 0.3,
          "stroke": "#e6761b",
          "stroke-width": "2",
          "stroke-opacity": 0.9
        }
      }]
  } 
    '.}.'
  ';

  $write = file_put_contents( $dir , $data_for_write );
  if($write) { $info = "Запись прошла";} else {$info = "Запись не прошла";}
  echo $info;
}

the error is in a piece of code

$data_for_write ='
  {
    "type": "FeatureCollection",
    "metadata": {
      "name": "Карта торгового центра",
      "creator": "Паблито SWP",
      "description": "Сквозь бесонные ночи была сделана эта карта. Пожалуйста не сломайте её!"
    },
  '.
    while($ob = $res->GetNextElement()){
      $arFields = $ob->GetFields();
      $arProps = $ob->GetProperties();
  .'
      "features": [{
        "type": "Feature",
        "id": "'.echo $arFields['ID'].'",
        "geometry": {
          "type": "Polygon",
          "coordinates": "'.echo $arProps['PROPERTIES']['COORDINATES']['VALUE'].'"
        },
        "properties": {
          "description": "'.echo $arFields['NAME'].'",
          "fill": "#ff931e",
          "fill-opacity": 0.3,
          "stroke": "#e6761b",
          "stroke-width": "2",
          "stroke-opacity": 0.9
        }
      }]
  } 
    '.}.'
  ';

Answer 1

The error, as usual, is in the DNA. Joke.
Remember for the rest of your life:
JSON is NEVER, under any circumstances, written by hand
. Type it in big letters and hang it on your monitor.
To get JSON, in PHP you make an array , which you then output using json_encode

Answer 2

You receive data from the infoblock, you need to send it in the form of json somewhere to someone, but you have syntax errors when generating json.
You need to use a validator to check.
It helps a lot to detect extra or missing characters, compare the result with examples from the documentation.
This is quite ugly:

spoiler

$data_for_write ='
  {
    "type": "FeatureCollection",
    "metadata": {
      "name": "Карта торгового центра",
      "creator": "SWP",
      "description": ""
    },
  '.
    while($ob = $res->GetNextElement()){
      $arFields = $ob->GetFields();
      $arProps = $ob->GetProperties();
  .'
      "features": [{

First collect everything in an array:
Example

spoiler

$data = array('items' =>array(
array(
'description' => $description, 
'category_id' => $category_id, 
'name' => 'Карта торгового центра',
'offer_id' => $offer_id,
'price' => $price,
'old_price' => $old_price,