Add the “input hidden” field type to the EDD settings

function edd_hidden_callback( $args ) {

	global $edd_options;

	if ( isset( $edd_options[ $args['id'] ] ) )

		$value = $edd_options[ $args['id'] ];

	else

		$value = isset( $args['std'] ) ? $args['std'] : '';

	$size = ( isset( $args['size'] ) && ! is_null( $args['size'] ) ) ? $args['size'] : 'regular';

	$html = '<input type="hidden" class="' . $size . '-text" id="edd_settings[' . $args['id'] . ']" name="edd_settings[' . $args['id'] . ']" value="' . esc_attr( stripslashes( $value ) ) . '"/>';

	echo $html;

}