Wait... you are trying to post your website INTO Ebays? Just include a URL. You can't touch their webservers.
yes he tries to embed /iframe his website/game into ebay description... its truly impossible ebay doesn't let embed codes. however they do let video embed codes from youtube... so it might be possible... he only needs to fake the embed to look like its youtube... which it would be easy if ebays system worked on a simple word detection then he just needed to change the embed name to class="youtube.something.gibirrish" and should have'd work, but it wont ebay doesn't allows it, since it seems on the discussion from back in 2016 that ebay basically deprecated all embed forms from their website.
so then gumshoe2029 solution is the best. just add a link to your website in the description. like
Play the demo <a href="yourlink"> >> here << </a>[/code:1juxw6r8]
if the description takes html code then should take also css so you could also case everything in a more powerful thing like this
<strong style="color: yourcolor;">Play the demo <u><a href="yourlink" style="text-decoration: none;"> >> here << </a></u></strong>
(you can place the color in what format you want either text like blue,red etc... or code FFF123 or even #321444)
[url=https://productforums.google.com/forum/#!topic/youtube/ZFkg_Jqb5t8]https://productforums.google.com/forum/ ... Fkg_Jqb5t8[/url] see embed code for ebay.
i tried adding a product in listing this is what i got from ebay
so to OP forget about embeding something on ebay just place a link. not even a hyperlink just a link