meta tags – iOS Smart App Banner on a Squarespace website

Apple shows that adding this meta tag to the head element of a page on a website would make the Smart App Banner appear when that page is visited on an iOS mobile device:

<meta name="apple-itunes-app" content="app-id=myAppStoreID, app-argument=myURL">

(app-argument is optional)

I wasn’t sure if this would be possible with a Squarespace site but they do offer “code injection” into the header:

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On Squarespace forums I saw the suggestion to format the meta tag in this fashion:

var meta = document.createElement('meta');
meta.name = 'apple-itunes-app';
meta.content = 'app-id=myAppStoreID, app-argument=';
document.getElementsByTagName('head')(0).appendChild(meta);

If I look at the source of https://www.peekaboo.mobi I can see this meta tag in there, but no banner appears when visiting the site on an iOS device.

Can you see anything that is wrong with my implementation here? Is Squarespace not actually injecting it into the right part of the page for it to work? I see a <div id="mobile-header"> in the page source…

Any help or guidance would be appreciated. Thanks!