Custom HTML field with iframe code

Hi,
I would like to put a different iframe field on every website. I have created a custom field but when I choose text area or other field looks like on the attachment after the <script> rest oh the code is visible on frontend website.

When I choose custom HTML the field is not available screenshot also in the attachment.

Screen

<div>
<div id="salesmanago-Iframe_e6f9b551-ca43-4b16-a9e6-2d4f9c95be1e"></div>
<script>
(function() {
var smIframeParentElem = document.getElementById("salesmanago-Iframe_e6f9b551-ca43-4b16-a9e6-2d4f9c95be1e");
var smIframeElem = document.createElement("iframe");
smIframeElem.src = "https://www.salesmanago.pl/mscf/3v8e84qpbrdlvrt9/default/ENG-BCGLOBALAPPS-MDMS.htm?" + Date.now() + '"';
smIframeElem.style.margin = "0";
smIframeElem.style.padding = "0";
smIframeElem.width = "500";
smIframeElem.height = "650";
smIframeElem.style.overflowY = "hidden";
smIframeElem.style.overflowX = "hidden";
smIframeElem.style.maxWidth = "100%";
smIframeElem.style.background = "transparent";
smIframeElem.style.border = "none";
smIframeParentElem.appendChild(smIframeElem);
}());
</script>
</div>