Shortcode Coding not working

Can you help me figure out what’s wrong with this coding????

// Add Shortcode
function book_display_shortcode( $atts ) {
	extract( shortcode_atts(
		array(
			'author' => 'default',
			'type' => 'products',
		), $atts ) );

$args = array (
	'post_type' => $type,
	'tag_name' => $author,
	);
$book_query = new WP_Query( $args );
ob_start();
?>
<div class="books-display">
<?php if ( $book_query->have_posts() ) {
	while ( $book_query->have_posts() ) {
		$book_query->the_post();

		<a> " > <?phpget_the_post_thumbnail($post_id, 'thumbnail'); ?> </a>

		}
		} else {  // no posts found 

		}
		wp_reset_postdata(); ?>
		</div>
		<?php return_ob_get_clean(); 

}
add_shortcode( 'books', 'book_display_shortcode' );