Resource interpreted as Document but transferred with MIME type application/zip
Solution 1:
You can specify the HTML5 download attribute in your <a> tag.
<a href="http://example.com/archive.zip" download>Export</a>
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/a#attr-download
Solution 2:
In your request header, you have sent Content-Type: text/html which means that you'd like to interpret the response as HTML. Now if even server send you PDF files, your browser tries to understand it as HTML. That's the problem. I'm searching to see what the reason could be. :)