How to add an admin notice upon post save/update

I have a post type the uses post_save to take the address from the post-meta and retrieve the lat/lng coordinates from the Google API. I need a way of notifying the user if there was an issue with retrieving the coordintes. I tried using admin_notices, but nothing displayed:

public static function update_notice() {
  echo "<div class="error"><p>Failed to retrieve coordinates. Please check key and address.<p></div>";
  remove_action('admin_notices', 'update_notice');
}

add_action('admin_notices', array('GeoPost', 'update_notice'));

I’m not sure if I’m using it incorrectly or in the wrong context. To be clear, in the actual code the add_action is in another function in the same class. That’s working fine.

The reason this doesn’t work is because there is a redirection happening after the save_post action. One way you can acheive want you want is by implementing a quick work around using query vars.

Here is a sample class to demonstrate:

class My_Awesome_Plugin {
  public function __construct(){
   add_action( 'save_post', array( $this, 'save_post' ) );
   add_action( 'admin_notices', array( $this, 'admin_notices' ) );
  }

  public function save_post( $post_id, $post, $update ) {
   // Do you stuff here
   // ...

   // Add your query var if the coordinates are not retreive correctly.
   add_filter( 'redirect_post_location', array( $this, 'add_notice_query_var' ), 99 );
  }

  public function add_notice_query_var( $location ) {
   remove_filter( 'redirect_post_location', array( $this, 'add_notice_query_var' ), 99 );
   return add_query_arg( array( 'YOUR_QUERY_VAR' => 'ID' ), $location );
  }

  public function admin_notices() {
   if ( ! isset( $_GET['YOUR_QUERY_VAR'] ) ) {
     return;
   }
   ?>
   <div class="updated">
      <p><?php esc_html_e( 'YOUR MESSAGE', 'text-domain' ); ?></p>
   </div>
   <?php
  }
}

Hope this helps you a little bit.
Cheers