For banner integration on your site you need to insert code below
<iframe id="cardbit_banner" width="550px" height="350px" style="border:0"></iframe>

<script type="text/javascript">

    let params = [
        'referral_id=777777',
        'return_url=https://gmail.com',
        'border=1',
    ];

    let http = new XMLHttpRequest();
    let url = 'https://my.cardbit.io/crypto_to_card_sender';
    let paramsString = '?' + params.join('&');
    http.open('GET', url + paramsString, true);
    http.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');

    http.onreadystatechange = function() {

        if(http.readyState === 4 && http.status === 200) {

            let doc = document.getElementById('cardbit_banner').contentWindow.document;
            doc.write(http.responseText);
        }
    };

    http.send(params);

</script>
        

Javascript code parameters: