CORS Error with JS and not with PHP when using API [duplicate]

Question

I'm using the auspost.com API to get a location from a Post Code - it works perfectly with PHP (on Load) - but not JS (on Form Change) - I'm new to APIs any help would be appreciated!

$curl = curl_init();

curl_setopt_array($curl, array(
    CURLOPT_URL => 'https://digitalapi.auspost.com.au/postcode/search.json?q=3008',
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_ENCODING => '',
    CURLOPT_MAXREDIRS => 10,
    CURLOPT_TIMEOUT => 0,
    CURLOPT_FOLLOWLOCATION => true,
    CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
    CURLOPT_CUSTOMREQUEST => 'GET',
    CURLOPT_HTTPHEADER => array(
        'AUTH-KEY: MY_KEY_HERE'
    ),
));

$response = curl_exec($curl);

curl_close($curl);
echo $response;

The above works perfectly!

...this does not, I get the following error: MY_DOMAIN is not allowed by Access-Control-Allow-Origin. Status code: 200

var myHeaders = new Headers();
    myHeaders.append("AUTH-KEY", "MY_AUTH_KEY");

var requestOptions = {
    method: 'GET',
    headers: myHeaders,
    redirect: 'follow'
};

fetch("https://digitalapi.auspost.com.au/postcode/search.json?q=3008", requestOptions)
    .then(response => response.text())
    .then(result => console.log(result))
    .catch(error => console.log('error', error));

Since I have seen other questions referencing CORS policy - but I don't have control over the hosting or domain of the API - Is there anything I can do ay MY end to fix this?