PHP to download generated CSV not pushing to the browser for download

Question

I have this function which generates a CSV and stores on the server (this works fine) however it is not pushing to the browser for the user to download, can anyone see why?

It is also putting the data into multiple sections like;

invoice details

customer details

invoice items

I would prefer if this put all the data onto 1 line rather than 3 sections but not sure how to do this.

Function:

// download invoice csv sheet
if ($action == 'download_csv'){

    header("Content-type: text/csv"); 

    // Connect to the database
    $mysqli = new mysqli(DATABASE_HOST, DATABASE_USER, DATABASE_PASS, DATABASE_NAME);

    // output any connection error
    if ($mysqli->connect_error) {
        die('Error : ('.$mysqli->connect_errno .') '. $mysqli->connect_error);
    }

    $tables = array('invoices', 'customers', 'invoice_items'); // array of tables need to export

    $file_name = 'invoice-export-'.date('d-m-Y').'.csv';   // file name
    $file_path = 'downloads/'.$file_name; // file path

    $file = fopen($file_path, "w"); // open a file in write mode
    chmod($file_path, 0777);    // set the file permission

    // loop for tables
    foreach($tables as $table) {
        $table_column = array();
        $query_table_columns = "SHOW COLUMNS FROM $table";

        // fetch table field names
        if ($result_column = mysqli_query($mysqli, $query_table_columns)) {
            while ($column = $result_column->fetch_row()) {
                $table_column[] = $column[0];
            }
        }

        // Format array as CSV and write to file pointer
        fputcsv($file, $table_column, ",", '"');

        $query_table_columns_data = "SELECT * FROM $table";

        if ($result_column_data = mysqli_query($mysqli, $query_table_columns_data)) {

            // fetch table fields data
            while ($column_data = $result_column_data->fetch_row()) {
                $table_column_data = array();
                foreach($column_data as $data) {
                    $table_column_data[] = $data;
                }

                // Format array as CSV and write to file pointer
                fputcsv($file, $table_column_data, ",", '"');
            }
        }
    }

    // close file pointer
    fclose($file);

    // ask either save or open
    header("Pragma: public");
    header("Expires: 0");
    header("Content-Type: application/octet-stream");
    header("Content-Disposition: attachment; filename='{$file_name}';" );
    header("Content-Transfer-Encoding: binary");

    // open a saved file to read data
    $fhandle = fopen($file_path, 'r');
    fpassthru($fhandle);
    fclose($fhandle);
    $mysqli->close();
    die;

}

JS

function downloadCSV(action) {

        jQuery.ajax({

            url: 'response.php',
            type: 'POST',
            data: action,
            dataType: 'json',
            success: function(data){
                $("#response .message").html("<strong>Success</strong>: CSV has been successfully generated and also been stored in the downloads/ directory.");
                $("#response").removeClass("alert-warning").addClass("alert-success").fadeIn();
                $("html, body").animate({ scrollTop: $('#response').offset().top }, 1000);
            },
            error: function(data){
                $("#response .message").html("<strong>Error</strong>: Oppps there has been a problem, please try again.");
                $("#response").removeClass("alert-success").addClass("alert-warning").fadeIn();
                $("html, body").animate({ scrollTop: $('#response').offset().top }, 1000);
            } 
        });

    }