Thank you for your reply. From Ken's answer: "If the website has functionality to give you the embed code or an embed URL, then you can use that URL successfully" Unfortunately in my case, the url's that I'm using come directly from a column in the data from the Airbnb database (Get the Data - Inside Airbnb. Adding data to the debate. ), and the "a0.muscache.com" comes up with a denial error message when accessed directly.
So I have no idea if this will make a difference, but I noticed one of the links in that article mentioned that https was the issue. I created a calculated field off of your picture_url field that replaced "https:" with "http:". I updated the dashboard action to use that field too.
The field with these changes is attached. The pictures still show up on desktop. It's possible they may show up on desktop over http, but I'm not really sure. It may not do anything.