уже советовали, выведите тип файла в сообщение об ошибке
// Allowed file extension types
$allowed = array();
$extension_allowed = preg_replace('~\r?\n~', "\n", $this->config->get('config_file_ext_allowed'));
$filetypes = explode("\n", $extension_allowed);
foreach ($filetypes as $filetype) {
$allowed[] = trim($filetype);
}
if (!in_array(strtolower(substr(strrchr($filename, '.'), 1)), $allowed)) {
$json['error'] = $this->language->get('error_filetype') . strtolower(substr(strrchr($filename, '.'), 1));
}
// Allowed file mime types
$allowed = array();
$mime_allowed = preg_replace('~\r?\n~', "\n", $this->config->get('config_file_mime_allowed'));
$filetypes = explode("\n", $mime_allowed);
foreach ($filetypes as $filetype) {
$allowed[] = trim($filetype);
}
if (!in_array($this->request->files['file']['type'], $allowed)) {
$json['error'] = $this->language->get('error_filetype') . $this->request->files['file']['type'] ;
}
файл /admin/controller/catalog/download.php