You've embedded an HTML code in your Email Marketing, but when you send your test Email Marketing it doesn't show up! This likely means that your HTML code is actually an iframe.
You can determine if your code is an iframe by looking at the code itself. If it's an iframe, it will always open and close with this code: <iframe src="url" title="description"></iframe>
Iframes are not supported by most email providers. While iframes are viewable on websites (ie. on Keela), they won't appear in your inbox via email. This is because a website is 'live', meaning that it can be viewed by any one with access to the url. When content is changed by the owner, all website visitors will see those changes. In comparison, e-mails are 'frozen'. They are stored in your secure inbox and the code within the email doesn't change.
The 'passive' e-mail content doesn't interact well with the content of an iframe, which can change over time. In addition, because iframes load content from an external website, they can be more easily exposed to viruses and corruption. As a result, most email service providers do not allow emails with iframes and will automatically remove this content from the Email Marketing.