When you say you provide a zip file to the developer, it sounds to me as if either something has gone wrong with the zip operation, or the developer hasn't unzipped it properly.
From your side, I'd say to take the zip and unzip it on your own machine. Then test. Does it work then? If so, you know the developer is doing something wonky on their side after you give them the file.
If it still doesn't work after YOU unzip it, then of course you have some detective work to do with your zip package to sort what you are doing wrong.
Yep, when I unzip the zip file (same one I sent to the developer) to a clean folder on my machine and launch the help, everything displays & links work as they should. So I'll double-check with the developer.
Check what browser they’re using – that may have an impact on displaying/not-displaying topic content
From the web server, the files don't open correctly in any browser. From the developer's desktop, the files open correctly in Firefox, but not Chrome or Safari. From my desktop, the files open correctly in Firefox and IE. I haven't tested them in Chrome or Safari.