Just had a situation with sending a file to a browser with POST request and it kept erroring with "Failed - Network error"

<?php 
// post request
$barcodefile  = 'barcode.pdf';
return $response->withFile(TMP . '$barcodefile, ['download' => true, 'name'=> 'barcode.pdf'])->withType('pdf');

The fix was to change the request for the file download from a POST request to a GET request

When I Googled the error the suggestions consisted of change Browsers, disable or re-configure anti-virus or reset your Browser to its defaults.

Once I changed the request action to GET it downloaded fine. Not sure why but it is a fix.