how can i post formatted message to api create?

I need to know how can I post formatted message to uvdesk api create.
I tried to send message with full html tags, and all html tags were sanitized.
I tried again using php `htmlentities()` `htmlspecialchars()`, converting html tags (limited to `p`, `br` and `a`) to ascii counterpart but it is also sanitized.
Can you please help me? 
Thanks in advance