Uncaught exception "DOMException" with message "Not Found Error" XPATH

Hello,

Below is an example of an XML and PHP file I'm developing, I'm trying
to insertBefore into the XML file butI continue to get this error:

Fatal error: Uncaught exception 'DOMException' with message 'Not Found
Error' in /home/.boots/rddesign/forttryon.com/availabilities/
editor_adjustment.php:100

All help is appreciated!








000000
000000
000000
000000
000000


4489 5G
400
$182,500.00
Available
Studio-J





000000
000000
000000
000000
000000


257 6D
575
$299,125.00
Contract Signed
1BR-H





000000
000000
000000
000000
000000


259 7D
900
$303,500.00
Available
2BR-I.






XML>


$dom = new DomDocument();
$dom->load("testData.xml");
$dom->preserveWhitespace = true;

$xpath = new DomXPath($dom);

//$availabilities = $xpath->query("/availabilities/
unit[@type='Studios']/availability")->item(0);
$availabilities = $xpath->query("/availabilities/
unit[@type='Studios']/availability/name")->item(0);
$availability = $dom->createElement('availability','helloWorld');

$dom->insertBefore($availability, $availabilities);
$dom->save("testData.xml");

?>