Can't get xml from php

Question

I've been trying to get data from my database into a table on my website using js/php but I can't get the php to give a valid xml to the script. This is the php code:

    <?php
    $serverName = "localhost";
    $userName = "***";
    $password = "***";
    $DBName = "DataBase1";
    
    // Connect to DB
    $connection = mysqli_connect($serverName, $userName, $password, $DBName);
    if (!$connection)
    {
        die("Connection failed: " . mysqli_connect_error());
    } else {
        //echo "Connected to DB<br>";
    }
    
    // Collect data
    $selectionSD = $connection->query("SELECT * FROM `SensorData`");
    $selectionSL = $connection->query("SELECT * FROM `SensorLog`");
    
    // Generating XML file
    //$xmlSD = new XMLWriter();
    //$xmlSD->openUri("php://output");
    //$xmlSD->startDocument();
    //$xmlSD->setIndent(true);
    //$xmlSD->startElement("SensorDataTable");
    //while ($row = mysqli_fetch_assoc($selectionSD))
    //{
    //  $xmlSD->startElement("SensorData");
    //      $xmlSD->startElement("ID");
    //          $xmlSD->writeRaw($row["ID"]);
    //      $xmlSD->endElement();
    //      $xmlSD->startElement("SID");
    //          $xmlSD->writeRaw($row["SID"]);
    //      $xmlSD->endElement();
    //      $xmlSD->startElement("Value");
    //          $xmlSD->writeRaw($row["Value"]);
    //      $xmlSD->endElement();
    //      $xmlSD->startElement("Comment");
    //          $xmlSD->writeRaw($row["Comment"]);
    //      $xmlSD->endElement();
    //      $xmlSD->startElement("DateTime");
    //          $xmlSD->writeRaw($row["DateTime"]);
    //      $xmlSD->endElement();
    //  $xmlSD->endElement();
    //}
    //$xmlSD->endElement();
    //header("Content-type: text/xml");
    //$xmlSD->flush();
    //$xmlSD->endDocument();
    
    // Test code
    $document = new DOMDocument('1.0', 'utf-8');
    $document->formatOutput = true;
    
    $root = $document->createElement('SensorDataTable');
    $root = $document->appendChild($root);
    
    while ($row = mysqli_fetch_assoc($selectionSD))
    {
        $node = $document->createElement('SensorData');
        $node = $root->appendChild($node);
    
        // ID
        $dataNode = $document->createElement('ID');
        $dataNode = $node->appendChild($dataNode);
        $data = $document->createTextNode($row["ID"]);
        $data = $dataNode->appendChild($data);
        // SID
        $dataNode = $document->createElement('SID');
        $dataNode = $node->appendChild($dataNode);
        $data = $document->createTextNode($row["SID"]);
        $data = $dataNode->appendChild($data);
        // Value
        $dataNode = $document->createElement('Value');
        $dataNode = $node->appendChild($dataNode);
        $data = $document->createTextNode($row["Value"]);
        $data = $dataNode->appendChild($data);
        // Comment
        $dataNode = $document->createElement('Comment');
        $dataNode = $node->appendChild($dataNode);
        $data = $document->createTextNode($row["Comment"]);
        $data = $dataNode->appendChild($data);
        // DateTime
        $dataNode = $document->createElement('DateTime');
        $dataNode = $node->appendChild($dataNode);
        $data = $document->createTextNode($row["DateTime"]);
        $data = $dataNode->appendChild($data);
    }
    
    echo $document->saveXML();
    
    // Close DB connection
    $connection->close();
    ?>

I've tried to generate the xml a different way but no luck (the commented lines was what I tried first).

To get the xml into a table I use js with this code:

console.log(xml);
let i;
const xmlDoc = xml.responseXML;
if (xmlDoc === null) {
    console.log("Failed to get response.");
}
let table = "<tr><th>SID</th><th>Value</th></tr>";
const x = xmlDoc.getElementsByTagName("SensorData");
for (i = 0; i < x.length; i++) {
    table += "<tr><td class='center'>" +
        x[i].getElementsByTagName("SID")[0].childNodes[0].nodeValue +
        "</td><td class='center'>" +
        x[i].getElementsByTagName("Value")[0].childNodes[0].nodeValue +
        "</td></tr>";
}
console.log("Changing DB display");
document.getElementById("DB").innerHTML = table;

Where xml = the path to the php file.

When trying to run this it gives an error that xmlDoc is null. If I run this using an actual xml file on my drive it works fine.

If I call the php file directly and inspect the source it shows this:

<?xml version="1.0" encoding="utf-8"?>
<SensorDataTable>
  <SensorData>
    <ID>1</ID>
    <SID>1</SID>
    <Value>19.50</Value>
    <Comment>DHT_Temp</Comment>
    <DateTime>2021-10-04 12:57:51</DateTime>
  </SensorData>
  <SensorData>
    <ID>2</ID>
    <SID>2</SID>
    <Value>57.50</Value>
    <Comment>DHT_Humi</Comment>
    <DateTime>2021-10-04 12:57:55</DateTime>
  </SensorData>
  <SensorData>
    <ID>3</ID>
    <SID>1</SID>
    <Value>19.60</Value>
    <Comment>DHT_Temp</Comment>
    <DateTime>2021-10-04 12:58:29</DateTime>
  </SensorData>
  <SensorData>
    <ID>4</ID>
    <SID>2</SID>
    <Value>57.20</Value>
    <Comment>DHT_Humi</Comment>
    <DateTime>2021-10-04 12:58:32</DateTime>
  </SensorData>
</SensorDataTable>

How can I fix this issue, I’ve searched the web but the solutions I've come across did not work (creating the xml in a different way for example).

Fixed: change in the php code, added header("Content-type: text/xml"); back:

<?php
$serverName = "localhost";
$userName = "***";
$password = "***";
$DBName = "LIDAc";

// Connect to DB
$connection = mysqli_connect($serverName, $userName, $password, $DBName);
if (!$connection)
{
    die("Connection failed: " . mysqli_connect_error());
}

// Collect data
$selectionSD = $connection->query("SELECT * FROM `SensorData`");
$selectionSL = $connection->query("SELECT * FROM `SensorLog`");

// Generate XML file
$document = new DOMDocument('1.0', 'utf-8');
$document->formatOutput = true;

$root = $document->createElement('SensorDataTable');
$root = $document->appendChild($root);

while ($row = mysqli_fetch_assoc($selectionSD))
{
    $node = $document->createElement('SensorData');
    $node = $root->appendChild($node);

    // ID
    $dataNode = $document->createElement('ID');
    $dataNode = $node->appendChild($dataNode);
    $data = $document->createTextNode($row["ID"]);
    $data = $dataNode->appendChild($data);
    // SID
    $dataNode = $document->createElement('SID');
    $dataNode = $node->appendChild($dataNode);
    $data = $document->createTextNode($row["SID"]);
    $data = $dataNode->appendChild($data);
    // Value
    $dataNode = $document->createElement('Value');
    $dataNode = $node->appendChild($dataNode);
    $data = $document->createTextNode($row["Value"]);
    $data = $dataNode->appendChild($data);
    // Comment
    $dataNode = $document->createElement('Comment');
    $dataNode = $node->appendChild($dataNode);
    $data = $document->createTextNode($row["Comment"]);
    $data = $dataNode->appendChild($data);
    // DateTime
    $dataNode = $document->createElement('DateTime');
    $dataNode = $node->appendChild($dataNode);
    $data = $document->createTextNode($row["DateTime"]);
    $data = $dataNode->appendChild($data);
}

header("Content-type: text/xml");

echo $document->saveXML();

// Close DB connection
$connection->close();
?>