Error trying to add JavaScript to Azure B2C Local Signup Page

I have the following arbitrary JavaScript snippet on an HTML page stored in Azure Storage (using a screenshot to try to demonstrate, as far as I can see, that the syntax is correct):

The page loads, it is styled correctly and everything else you would expect, proving that it is configured correctly, CORS is set etc. But the JavaScript does not run. Instead I get this error:

unified:5 Uncaught SyntaxError: Unexpected token '&'
at br (unified?local=signup&[omitted_for_brevity])
at at (unified?local=signup&[omitted_for_brevity])
at i.fn.init.append (unified?local=signup&[omitted_for_brevity])
at unified?local=signup&[omitted_for_brevity]

This is presumably being caused by this:

Extra script caused by some kind of parse or encoding error on the original script tag.

If I load the file from storage container directly, it loads and the JavaScript fires with no problems. This tells me the HTML file is fine, so either:

• how I am loading it does not play nicely with B2C
• I have not configured something on the B2C side to allow JavaScript
• Something else

I have configured everything that I can see on the User Flow:

• Enable JavaScript enforcing page layout is set to On
• Path to custom HTML is set
• CORS is configured for the custom HTML

Has anyone seen this problem before or can see what I may have done wrong in how this is configured?

Edit: Am roughly following this guide: https://learn.microsoft.com/en-us/azure/active-directory-b2c/javascript-and-page-layout?pivots=b2c-user-flow

You need to include the script in the head tag of the page if you're using page layout version 2.1.21 or higher for the self-asserted, or when you're using unified sign-in and sign-up page layout version 2.1.10 or higher. See: https://learn.microsoft.com/en-gb/azure/active-directory-b2c/page-layout