I just heard back from Unbounce and here is what they said:
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Unfortunately taking a look into this shortcode, the issue appears to be that it does not seem to be valid HTML format to embed to the Unbounce pages. Because this is third-party code from s2member, we would not be able to troubleshoot this directly not having written the code ourselves. We would recommend returning back to your resource for this snippet and request a chunk of valid embedding HTML code for your ClickBank shopping cart buttons.
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How can I create valid embedding html code?
Thanks-