 <p>The <a href="https://en.wikipedia.org/wiki/List_of_HTTP_header_fields" rel="nofollow">content type</a> in a request header is the content of what you're <em>sending</em>. You're not sending an Excel file, you're requesting an excel file.</p> <p>When you send the <code>"application/x-www-form-urlencoded"</code> content type header, you're telling the server that your parameters must be read in the URL (<a href="https://www.w3.org/TR/html401/interact/forms.html#h-17.13.4.1" rel="nofollow">this is the standard way</a>).</p>