error Invalid argument supplied for foreach() for the second foreach in the code

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in my code below the data is extracted correctly but i still get the error Warning: Invalid argument supplied for foreach() for line 24 i.e foreach ($authorlist as $post)

below is my code

<?php

$all= get_posts(array('post_type' => 'books', 'numberposts' => -1,));

foreach ( $all as $post ) :  setup_postdata($post);

    if (!empty($post))
    {
     $booklink = array();

     $booklist = strip_tags(get_field('booklist')); 
               foreach ($booklist as $post) : setup_postdata($post);
                    if (!empty($post))
                        {
                        $booklink[] = strip_tags(get_field('booklink',$post));                                       
                        }
                endforeach;
                wp_reset_postdata();
echo $booklink[0];  

     $authorname = array();

     $authorlist = strip_tags(get_field('booklist')); 
               foreach ($authorlist as $post) : setup_postdata($post);
                    if (!empty($post))
                        {
                        $booklink[] = strip_tags(get_field('authorname',$post));                                       
                        }
                endforeach;
                wp_reset_postdata();
echo $authorname[0]; 

    }
endforeach;
?>

asked 46 secs ago

user3449454

20

error Invalid argument supplied for foreach() for the second foreach in the code