Zoom Contact Center Smart Embed (CCSE)- login fails

I am guessing we are making a pretty simple mistake, but it is a bit of a black box trying to see where.

We have requested the CCSE be added to our account, and it is there/configured…, and now we are attempting to invoke the smart embed on our own domain (pass protected unfortunately, but full URL is syndication dot doorifymls dot com/zoomtest
The frame invokes, but we error on login
On the invocation side we have tried several permutations of this:

<iframe
src="https://zoom.us/crm-int/callbar/?origin=syndication.doorifymls.com/zoomtest"
sandbox="allow-forms allow-popups allow-popups-to-escape-sandbox allow-scripts allow-same-origin allow-downloads"
allow=";autoplay;microphone;camera;display-capture;midi;encrypted-media;clipboard-write;"
id="zoom-embeddable-phone-iframe"
></iframe>

On the zoom side, our CCSE config simply points to the smart embed instance url syndication dot doorifymls dot com/zoomtest

Any pointers?