Function allow upload csv file for wordpres in function.php
define('ALLOW_UNFILTERED_UPLOADS', true);
function chutuoc_upload_mimes($mimes = array()) {
// Add a key and value for the CSV file type
$mimes['csv'] = "text/csv";
return $mimes;
}
add_action('upload_mimes', 'chutuoc_upload_mimes');