ioniklabs

Hope this helps.

The solution below expects an ACF checkbox option custom_author. If this is set to false the default WordPress author will be used, otherwise we populate the author object with values from ACF.

The below snippet can be placed in your theme’s functions.php file.

add_filter( 'instant_articles_authors', 'modify_instant_articles_authors', 50, 2 );

function modify_instant_articles_authors( $authors, $post_id ) {
    if ( get_field( 'custom_author', $post_id ) ) {
        $authors = array();
        $author = (object) [];
            $author->display_name = get_field( 'author_name', $post_id );
            $author->user_url = get_field( 'author_url', $post_id );
            $author->bio = get_field( 'author_bio', $post_id );
        $authors[] = $author;
    }
    return $authors;
}