How to allow fullscreen in embedded YouTube videos?

Hi! I've embedded a YouTube video into a chat response, and it works perfectly. However, I noticed that I cannot make the embedded video open in fullscreen. When I try, I get a message saying fullscreen unavailable. I checked the source code for the embedded video, and it's something like this:

<iframe style="min-width:300px;max-width:400px" src="YOUTUBE_URL"></iframe>

Is it possible to add the allowfullscreen attribute, like so:

<iframe style="min-width:300px;max-width:400px" src="YOUTUBE_URL" allowfullscreen></iframe>

Thanks!