"Warning: Use of undefined constant" in WP AVADA website header

Hello Guys,
I have thisi problem in my WP avada website today, this warning display on the header of my website, do you know how to solve this ? really appreciate.
“Warning: Use of undefined constant HTTP_USER_AGENT - assumed ‘HTTP_USER_AGENT’ (this will throw an Error in a future version of PHP) in /home/goodluxl/public_html/wp-content/themes/Avada/header.php on line 1”

Hi @sanfordzhen

Please make sure you are using the latest evrsion theme and your server php version is uptodate.

If the above things not solved please contact your purchased theme author, theme author will assist you.

How to contact an author to get support or for any technical query: