msargenttrue on "[Plugin: Frontend Uploader] Missing data for $_POST in fu_after_upload action"

I’m trying to retrieve the filenames of the uploaded files from the $_FILES array but I’m struggling.

print_r($_FILES); clearly works but when I try to loop through $_FILES I’m not getting anything.

Here’s the output I have from print_r($_FILES); after uploading a single file:

Array
(
    [files] => Array
        (
            [name] => Array
                (
                    [0] => testfile.pdf
                )

            [type] => Array
                (
                    [0] => application/pdf
                )

            [tmp_name] => Array
                (
                    [0] => /tmp/phpkC2Tsw
                )

            [error] => Array
                (
                    [0] => 0
                )

            [size] => Array
                (
                    [0] => 1119353
                )

        )

)

I've tried looping through the array 2 ways and I'm getting no output. Here's what I have in functions.php so far.

add_action( 'fu_after_upload', 'my_fu_after_upload', 10, 3 );
function my_fu_after_upload( $attachment_ids, $success, $post_id ) {

	echo "<pre>";
	print_r($_FILES);
	echo "</pre>";

	$count = count($_FILES['files']);
	for($i=0; $i<=$count; $i++) {
	  if ($_FILES['files'][$i]['size'])
	    echo $_FILES['files'][$i]['name']."\n";
	}

	foreach($_FILES['files'] as $file) {
	    echo $file['name']."\n";
	}
}

Ultimately, I'm trying to retrieve the link(s) of any uploaded file(s) immediately after the file(s) are uploaded. But I'm stuck at how to pull the data I need from $_FILES.

Thanks for any help.