iFrame embedding not working

I cannot embed a model into a WordPress site. I get “Embedding not allowed for …”
This happens on my site and I also tried it on w3schools.com
used a different browser and different models, always with the same result.

Any help?
Thanks in advance

Did you add www.w3schools.com ?
Please note that after changing the allowed embedding domains on your dashboard, it can take a few minutes for the information to propagate to your models.

Yes, I whitelisted both w3schools.com and my domain on different tests during the week with no luck. However, today everything is working ok !!!???

I now tried two things:

  1. embedded the iFrame code
  2. pasted the App Builder sharing link

Both seem to work fine.
What is the difference?

Many thanks, Alexander