Hi @ayeweb
That’s because the shortcode is trying to get the global $post variable on your site, which doesn’t have the correct post ID if you put it in a widget.
In this case, you need to modify the template where you show the widget (usually sidebar) and show the data manually like this:
// get the latest post
$latest_posts = get_posts("post_type=post&numberposts=1");
// show the custom field
echo the_field('p1', $latest_posts[0]->ID);
This page should give you more idea about it: https://www.advancedcustomfields.com/resources/displaying-custom-field-values-in-your-theme/.
I hope this makes sense 🙂
