SoapClient PHP code without WSDL from example CURL request - php

Question

I am trying to call a SOAP API using PHP and have been given the following example CURL call:
curl --location --request POST 'https://soapurl.test/mysoapcall'
--header 'Content-Type: application/xml'
--header 'client-id: <<your client id>>'
--header 'client-secret: <<your client secret>>'
--header 'Authorization: Bearer <<token>>'
--data-raw '<S:Envelope xmlns:S="http://schemas.xmlsoap.org/soap/envelope/" xmlns:env="http://schemas.xmlsoap.org/soap/envelope/">
<env:Header></env:Header>
<S:Body>
<ns0:getReturnedValues xmlns:ns0="https://soapurl.test/anotherurl1" xmlns:ns1="https://soapurl.test/anotherurl2">
<ns0:var1>100</ns0:var1>
<ns0:var2>XXX</ns0:var2>
</ns0:getReturnedValues>
</S:Body>
</S:Envelope>'
I can successfully call the above via Postman, but when I am writing the PHP code using SoapClient, I keep getting "One or more required API parameters are missing in the API request."
I know that I must have something wrong with how I am defining the SOAP headers or how I am defining the uri, but I can't work out what it is.
Here is my PHP code:
$client = new SoapClient(null, array('location' => "https://soapurl.test/mysoapcall",
'uri' => "https://soapurl.test/anotherurl1");
$ns = 'https://soapurl.test/anotherurl1';
$headers = array();
$headers[] = new SoapHeader($ns,
'client-id',
'my_client_id');
$headers[] = new SoapHeader($ns,
'client-secret',
'my_client_secret');
$headers[] = new SoapHeader($ns,
'Authorization',
'Bearer my_bearer_token');
$client->__setSoapHeaders($headers);
$client->__soapCall("getReturnedValues", array('var1'=>'100', 'var2' => 'XXX'));
$client->__soapCall("getReturnedValues", [
new \SoapParam('100', 'var1'),
new \SoapParam('XXX', 'var2')
]);
My PHP code generates the following request:
<?xml version="1.0" encoding="UTF-8"?>
<env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope" xmlns:enc="http://www.w3.org/2003/05/soap-encoding" xmlns:ns1="https://soapurl.test/anotherurl1" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<env:Body>
<ns1:getReturnedValues env:encodingStyle="http://www.w3.org/2003/05/soap-encoding">
<var1 xsi:type="xsd:string">100</var1>
<var2 xsi:type="xsd:string">XXX</var2>
</ns1:getReturnedValues>
</env:Body>
</env:Envelope>
Which is obviously not the same as the example I was supplied with.
I'm new to SOAP, so please can someone advise on what I am doing wrong? Many thanks