Thanks for your reply. I am deploying the Datapage on a self hosted WordPress website. I've tried it both using the Embed and WordPress (with plug-in) deploy methods.
I tested the direct link in Firefox, I did see the authentication fields. I then tried the page on Microsoft Edge and that worked. On a whim, I decided to try it again on Firefox and now the fields display! I really don't know how to explain it, but it probably has something to do with cache and/or cookies, which I did clear when previously testing.
I guess as long as it continues working it will be one of the great unsolved mysteries.
Thanks for you assistance!!