Problem with php syntax error

Hello, I am editing the plugin file and this is my php code

<div class="review-thumb relative">';
    $thumb = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'post-thumb' );
    $return_string .='<img itemprop="image" src="' . esc_url( $thumb['0'] ) .'" />

    <div class="review-thumb-credit">
    <?php echo get_post_meta($post->ID, "mvp_photo_credit", true); ?>
    </div><!--review-thumb-credit-->
</div><!--review-thumb-->

The first code executed successfully and I get the post thumbnail. But the second code ( review-thumb-credit ) causing issue and the output is
ID, "mvp_photo_credit", true); ?>
This is not the correct output. Anybody help me in this issue.