upload-field.php

<?php
// AnsPress upload field.
array(
  ...
  'type' => 'upload',
  'upload_options' => array(
    'allowed_mimes'   => ap_allowed_mimes(), // Or you can allow your own types.
    'max_files'       => 1, // Numbers of files allowed to upload.
    'multiple'        => false, // This must be true if you wish to upload multiple files.
    'label_deny_type' => __( 'This file type is not allowed to upload.', 'anspress-question-answer' ),
  ),
  ...
);