Error on advertisement set-up

I’m trying to set up the plugin on my website but I keep recieving an error message on facebook.

At the “advertisement code” section I used the following code:

<figure class=”op-ad”><iframe src=”https://www.adserver.com/ss;adtype=banner300x250&#8243; height=”300″ width=”250″></iframe></figure>

But my instant articles are not showing up on facebook, and there I got his message:

“Ad default template is not specified: Ad default template is not specified, use the last one in ad section block instead”