Responsive Wallpapers and Flex Skin ad products can only be purchased via a direct buy with the Publisher for the site the ad product will be served on. These ad products are not available via a programmatic buy.
Responsive Wallpapers and Flex Skins require specialized 3rd Party tags to display on the publisher's site, which are provided by the Flexitive team. These tags are tailored to fit the dimensions and layout of the site the wallpaper is hosted on.
For a list of sites that have run Flexitive Responsive Wallpapers or Flex skins in the past, check out this document.
If there is a site you would like to host a responsive wallpaper or Flex Skin on that is not listed as a site we've hosted one of these ad products on in the past, we may still be able to add it for you. For more information, reach out to us at firstname.lastname@example.org.