Wordpress how to send email confirmations on post status change

I have a custom post type called "Booking" in WP travel plugin. I want it to fire an event when i change the status of that custom post type from 'pending' to 'booked'.

The event should send a confirmation email to the user in question.

I tried the following :

function show_alert_msg( $new_status, $old_status, $post ) {
    if ( 'Booked' === $new_status && 'pending' !== $old_status && $post->post_type=='Booking' )
        
     {
         echo '<script>alert(Show message after transition to booked)</script>' ;
    }else{
        echo '<script>alert(failed)</script>' ;

    }
}
add_action( 'transition_post_status', 'show_alert_msg', 10, 3 );

but whenever i change the status nothing happens.

what i am doing wrong? and how can I approach this correctly so that when the booking status changes from pending to Booked, the confirmation email is sent to the user ?

It's because there are several bugs in your code!

• You're using WP travel plugin. This plugin register its custom post type as "itinerary-booking", but in your code, you're checking for a custom post type called "Booking" which doesn't exist, so that condition never returns true!

  You could navigate to this path:
  "your website folder > wp-content > plugins > wp-travel > inc"
  and open up class-post-types.php file on line 126 you see this register_post_type( 'itinerary-booking', $args );

• Also, you're using transition_post_status action hook which is used for the checking a post status. The status of pending and booked are custom post meta data and saved into the database under the wp_travel_booking_status name and have nothing to do with the post status itself! Which means it's totally different than what you're trying to do.

So, this filter hook transition_post_status is not responsible to pick up those statuses.

• Also, when trying to debug/test your code, specially on transition_post_status and save_post hooks, do NOT use javascript alert, console.log and/or php echo, print_r, var_dump etc. because when you hit those hooks, printing, echoing, alerting won't work. Just use php die function which will stop the app and lets you know that you hit the hook.

• Also capitalization matters! Make sure you're using the right capitalization for your values, for example, in this case, everything is lowercase. So keep an eye on that!

---

Now what can you do about it?

1. Well, you could change your hook to save_post action hook which means every time that you update your post, it'll fire!
2. You could change your conditional check to look for itinerary-booking custom post type.
3. Also you could use get_post_meta function, to check for your status change!

Now putting it all together, you could use the following code:

add_action( 'save_post', 'sending_email_confirmation_to_user');

function sending_email_confirmation_to_user( $post_id )
{

  if ( 'itinerary-booking' == get_post_type( $post_id ) ){

    $post_status_after_update = get_post_meta( $post_id, 'wp_travel_booking_status', true );

    if( 'booked' === $post_status_after_update ){
      die("Send your email here!");
    } else {
      die("your post status is not booked!");
    }
  }

}

Note:

• I used die statement just to give you an example, so make sure to replace die("Send your email here!"); with your custom function that sends out emails!
• Status of booked is lowercase, so don't change it to uppercase like the one you tried in your code! Otherwise it won't work!
• When your post status is not "booked", you don't have to do anything, i used die("your post status is not booked!"); just to give you an example!

---

Update

When you use save_post hook, it runs every time you update your custom post data, BUT you do NOT want to send an email every single time. Right?

When you change the status from 'pending' to 'booked' you could save a meta data in the database so that you know you've already sent an email confirmation and you don't want to send another email. You could do that using update_post_meta function.

add_action( 'save_post', 'sending_email_confirmation_to_user');

function sending_email_confirmation_to_user( $post_id )
{

  if ( 'itinerary-booking' == get_post_type( $post_id ) ){

    $post_email_status = get_post_meta( $post_id, 'custom_confirmation_email', true );
    $post_status_after_update = get_post_meta( $post_id, 'wp_travel_booking_status', true );

    if( 'booked' === $post_status_after_update && empty( $post_email_status )){
      $email_sent = update_post_meta( $post_id, 'custom_confirmation_email', 'sent-at-'. date( 'M_d_Y-H_i_s' ) );
      die("Send your email here!");
    } 
  }

}

Note:

• This will make sure that you only send your email confirmation once!
• If the email confirmation data is empty in the database, it'll send the email and update the value in the database and won't send extra emails.
• Also, I've stored a meta data in your database called custom_confirmation_email and used 'sent-at-'. date('M_d_Y-H_i_s') as its value which looks like this: sent-at-Oct_01_2021-17_42_42 which is the date and time when the status changed from 'pending' to 'booked' for the first time.

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All of the snippets and explanations have been fully tested and work!