When you try to embed content from other websites in SharePoint Online, you may receive the following error message: “Embedding content from this website isn’t allowed, but your admin can change this setting. They will need to add ‘[URL domain address]‘ to the list of sites that are allowed.” 

The following error message occurs when the domain does not appear on the “approved domain list” in SharePoint:

How to add a Domain to the Approved Domain List 

1. In SharePoint, click on the settings Gear icon > Site Information.
   
   
   
2. On the next screen, click View all site settings.
   
   
   
3. On the Site Settings page, under Site Collection Administration, click on HTML Field Security.
   On the next screen, you will see a list of approved domains that are already part of the “approved domains” list.
   
   
4. Add the domain you want to embed.
5. click Add > OK.