Thank you for your help. It works.
I have two questions.
1. You inserted this code.
 is User ID. I have another short code .  is First Name.
If I replace  to , will it work?
2. I tested send message. Message box is working.
However, Service buyer, service provider and admin do not get any email.
I set example@domain name for ‘from email’ on the setting.
How can i fix?