CLIENT SIDE:
function downFile(){
var formData = new FormData();
formData.set('email','$email');
formData.set('gf_line','$line');
formData.set('code','$code');
var xhttp = new XMLHttpRequest();
	xhttp.onreadystatechange = function() {
	if (this.readyState == 4){
		if (this.status == 200) {
			if (xhttp.responseType == 'text' || xhttp.responseType == '') {
			alert('Sorry, but there appears to be an error\\nThis could be:\\n\\n- The email address entered\\ndoes not match the email in database\\n\\n- The code you entered is incorrect\\n\\nPlease check your details, and try again');
                	window.history.back();
                	return false;
                	}
                	else if (xhttp.responseType == 'blob'){
			// Create a new Blob object using the response data of the onload object
			var blob = new Blob([this.response], {type: 'application/zip'});
			//Create a link element, hide it, direct it towards the blob, and then 'click' it programatically
			let a = document.createElement("a");
			a.style = "display: none";
			document.body.appendChild(a);
			//Create a DOMString representing the blob and point the link element towards it
			let url = window.URL.createObjectURL(blob);
			a.href = url;
			a.download = 'Branded Files.zip';
			//programatically click the link to trigger the download
			a.click();
			//release the reference to the file by revoking the Object URL
			window.URL.revokeObjectURL(url);
			}
		}
        }

    xhttp.open("POST", "download.pl", true);
    xhttp.send(formData);
}
</script>

SERVER SIDE:
...
..
.
if ($inEmail ne $email){
print "content-type: text/html\n\n";
print "500";		# Returned as a "TEXT" response
exit;
}
else{
open FILE, "<", "../data/$user/$dir/$code/$fileCode.zip";
binmode FILE;
while(<FILE>){
$file.=$_;
}
close FILE;
#print "content-type: text/html\n\n";
#print "content-type: application/zip\n";
#print "content-disposition: attachment; filename='Branded Files'\n\n";
print $file;		# Returned as a "BLOB" response