"File preview not available" Application Domain not Authorized when Client ID is for the Domain

With this set of Document Cloud PDF Embed API Client Credentials:
CLIENT ID (API KEY) 411046add6cc41639dd27f9f9b827bab

APPLICATION DOMAIN preview.rpsl.org.uk

Why does this code on preview.rpsl.org.uk:
<div id="adobe-dc-view">&nbsp;</div>
<!-- Light Box --><script src="https://documentcloud.adobe.com/view-sdk/main.js"></script><script type="text/javascript">
document.addEventListener("adobe_dc_view_sdk.ready", function(){
var adobeDCView = new AdobeDC.View({clientId: "411046add6cc41639dd27f9f9b827bab", divId: "adobe-dc-view"});
adobeDCView.previewFile({
content:{location: {url: "https://documentcloud.adobe.com/view-sdk-demo/PDFs/Bodea Brochure.pdf"}},
metaData:{fileName: "Bodea Brochure.pdf"}
}, {embedMode: "LIGHT_BOX"});
});
</script>

Fail with the message indicating that the provided Client ID is not authorized:

File preview not available
This application domain (https://preview.rpsl.org.uk) is not authorized to use the provided PDF Embed API Client ID.

This makes no apparent sense to me - so I am puzzled. Any ideas, please?