Embedding <video> inside <iframe> works in emulator, but not on the actual TV


I have a simple Tizen webapp that works fine in emulator, but not on my Samsung signage TV (SSSP6).

        <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">   
        <meta charset="UTF-8" />
        <link rel="stylesheet" type="text/css" href="css/style.css" />
    	<div class='embed-container'>
        	<iframe width="100%" height="100%" sandbox="allow-same-origin allow-top-navigation allow-forms allow-scripts allow-popups" src="https://ad-presenter-staging.herokuapp.com/betsonglobal"></iframe>

If I replace the <iframe> with an actual <video> with the same content as what’s in src, then it works fine in both emulator and on the TV.

How do I go about debugging this?