position:fixed;

In the code the position is already been set to fixed,

position:fixed;

but still it is not working.

Here is the code I have ,

<script>
    var partner_phone = '+xxxxxxxxxxxx';
    var welcomeMessage = "Hello, I am interested in your products and I would like to get more informations about it!";

    //Wait for jquery to load before executing code
    addEventListener('JqueryLoaded', function(e) {
        //Type or paste your jquery code here

        if (partner_phone != "") {

            $("#WhatsappChat").show();

            $("#WhatsappChat").click(function() {
                openInNewTab("https://api.whatsapp.com/send?phone=" + partner_phone + "&text=" + encodeURIComponent(welcomeMessage))
            });

        }

    }, false);

    function openInNewTab(url) {
        var win = window.open(url, '_blank');
        win.focus();
    }
</script>


<div id="WhatsappChat" style="display:none;z-index:1000;position:fixed;right:25px;bottom:200px;background-position:initial;background-size:initial;background-repeat:initial;background-attachment:initial;background-origin:initial;background-clip:initial;background-color:#4fce5d;padding:20px;border-radius:100px;box-shadow:#8c8c8c 1px 1px 1px;outline:0;background-image:url('')"
    class="Bubble__BubbleComponent-sc-83hmjh-2 cVvwjZ" type="bubble" tabindex="0" role="button">
    <div class="Icon__Component-sc-6s5exc-0 jUeIxo Bubble__StyledIcon-sc-83hmjh-1 OycIV">
        <svg viewBox="0 0 90 90" fill="white" width="15" height="15">
                        <path d="M90,43.841c0,24.213-19.779,43.841-44.182,43.841c-7.747,0-15.025-1.98-21.357-5.455L0,90l7.975-23.522   c-4.023-6.606-6.34-14.354-6.34-22.637C1.635,19.628,21.416,0,45.818,0C70.223,0,90,19.628,90,43.841z M45.818,6.982   c-20.484,0-37.146,16.535-37.146,36.859c0,8.065,2.629,15.534,7.076,21.61L11.107,79.14l14.275-4.537   c5.865,3.851,12.891,6.097,20.437,6.097c20.481,0,37.146-16.533,37.146-36.857S66.301,6.982,45.818,6.982z M68.129,53.938   c-0.273-0.447-0.994-0.717-2.076-1.254c-1.084-0.537-6.41-3.138-7.4-3.495c-0.993-0.358-1.717-0.538-2.438,0.537   c-0.721,1.076-2.797,3.495-3.43,4.212c-0.632,0.719-1.263,0.809-2.347,0.271c-1.082-0.537-4.571-1.673-8.708-5.333   c-3.219-2.848-5.393-6.364-6.025-7.441c-0.631-1.075-0.066-1.656,0.475-2.191c0.488-0.482,1.084-1.255,1.625-1.882   c0.543-0.628,0.723-1.075,1.082-1.793c0.363-0.717,0.182-1.344-0.09-1.883c-0.27-0.537-2.438-5.825-3.34-7.977   c-0.902-2.15-1.803-1.792-2.436-1.792c-0.631,0-1.354-0.09-2.076-0.09c-0.722,0-1.896,0.269-2.889,1.344   c-0.992,1.076-3.789,3.676-3.789,8.963c0,5.288,3.879,10.397,4.422,11.113c0.541,0.716,7.49,11.92,18.5,16.223   C58.2,65.771,58.2,64.336,60.186,64.156c1.984-0.179,6.406-2.599,7.312-5.107C68.398,56.537,68.398,54.386,68.129,53.938z">
                        </path>
                      </svg>
    </div>
    <div class="Bubble__BubbleText-sc-83hmjh-0 fLLPCu">
    </div>
    </div>```

It seems you're talking about custom code. Can you share a link or at least a screenshot of what you have?

In general to have an element fixed in a particular position you would just need to set it position to fixed.