Add Category After Date From ACF Date Picker Field Has Expired

Need to add category to custom post type entries after a date from an acf date picker field has passed.

I found the following code which almost does the same thing. The difference is that it sets the expired post to draft instead of adding a category.

// Expire events
if ($expireTransient = get_transient($post-ID) === false) {
    set_transient($post-ID, 'set for 1 minutes', 1 * MINUTE_IN_SECONDS );
    $today = date('Ymd', current_time('timestamp', 0));
    $args = array(
        'post_type' = 'ausstellung',
        'posts_per_page' = 200,
        'post_status' = 'publish',
        'meta_query' = array(
            array(
                'key' = 'ende_datum',
                'value' = $today,
                'compare' = '='
            )
        )
    );
    $posts = get_posts($args);
    foreach( $posts as $post ) {
        if(get_field('ende_datum', $post-ID)) {
            $postdata = array(
                'ID' = $post-ID,
                'post_status' = 'draft',
            );
            wp_update_post($postdata);
        }
    }
}

This is how i changed the code – unfortunately it isn't working.

// Expire events
if ($expireTransient = get_transient($post-ID) === false) {
    set_transient($post-ID, 'set for 1 minutes', 1 * MINUTE_IN_SECONDS );
    $today = date('Ymd', current_time('timestamp', 0));
    $args = array(
        'post_type' = 'ausstellung',
        'posts_per_page' = 200,
        'post_status' = 'publish',
        'meta_query' = array(
            array(
                'key' = 'ende_datum',
                'value' = $today,
                'compare' = '='
            )
        )
    );
    $posts = get_posts($args);
    foreach( $posts as $post ) {
        if(get_field('ende_datum', $post-ID)) {
            $postdata = array( 'ID' = $post-ID, );
            $cat_ids = array( 32 );         
            wp_set_object_terms($postdata, $cat_ids, 'hf_cat_ausstellung');
        }
    }
}

The custom taxonomy is named hf_cat_ausstellung and is registered trough a plugin called happy files, the id of the term called past is 32.