Send notification (message)

Hi,

I see others plugins uses "notify_user($to, $from, $subject, $message);" for send notification. But it's dont work..

 

If i replace with "messages_send()" function, it's work.

1. What's the difference between "notify_user()" and "messages_send()" ?

2. Why "notify_user()" don't work ?

 

Good day!

Syntaxlb