Sniply uses iframe technology to load web pages and we only support sites that enable iframes on their pages. Sites with high security settings sometimes block iframes for security purposes. For example, banking portals and payment processing sites like PayPal are not supported by Sniply.
Many sites on the internet do support iframes and we're constantly working towards building support for more sites over time.
If you are the owner of a website that is not supported by Sniply and you would like to have your site supported, you can enable Sniply with a few simple steps here https://sniply.zendesk.com/hc/en-us/articles/204103485-It-says-my-website-isn-t-supported-how-can-I-fix-that-