Simply add admin notices for all post saving hooks. You can either set the notice using set_notice_status or wrap your hook with with_error_notice, then all the errors will be catched and send displayed as a notice on the admin UI.

Features

Gutenberg notices
Classic editor notices

Installation

composer require koko-ng/admin-notice

Examples

require 'vendor/autoload.php';

add_action('acf/save_post', \Admin_Notice\with_error_notice( 'my_acf_save_post') );
function my_acf_save_post( $post_id ) {

  // You can use `\Admin_Notice\Exception` to set a notice level.
  throw new \Admin_Notice\Exception("Error message", 0, \Admin_Notice\NoticeLevels::Warning);
}