get custom post type value in header.php [closed]

by

I’m observing three problems here.

1- Your anchors do not have a href attribute.

As you mentioned, the app_url field is a URL, and should be output in the href attribute of an anchor. So, this is how your anchor should look like:

<a href="https://wordpress.stackexchange.com/questions/293751/<?php echo esc_url( get_field("app_url' ) ); ?>">My Link</a>

Note that I’ve also escaped the value by using the esc_url() function, to eliminate invalid characters.

2- The get_field() function accepts a post ID.

The second parameter of the get_field() function accepts a post ID. So, let’s pass it to the function in the loop:

<?php 

    $args = array( 'post_type' => 'slider');
    $loop = new WP_Query( $args );
        while ( $loop->have_posts() ) : 
            $loop->the_post(); ?>
                <a href="https://wordpress.stackexchange.com/questions/293751/<?php echo esc_url( get_field("app_url', get_the_ID() ) ); ?>">
                    <?php the_title(); ?>
                </a><?php
        endwhile; 

?>

3- You forgot to use the PHP tags

Note that you didn’t have opening and closing PHP tags around your anchors in the loop ( The <?php and ?> tags ), and there was a missing a in your closing </a> tag.