add button to specific post

Assuming that the hook you have used is correct; below is the updated code which you can use:

function custom_listify_single_job_listing_actions_after() {

    global $post;

    if( $post->ID == 1464 ) {

        $url = get_post_meta( $post->ID, 'your_custom_meta_key', true );

        echo '<a href="' . esc_url( $url ) . '" class="button">My Button</a>';
    }
}
add_filter( 'listify_single_job_listing_actions_after', 'custom_listify_single_job_listing_actions_after' );

Let me know how it goes.