php errror message after installation

Hello,
after installing the data base and files of the web site i have the following message error at the top of the page.
Warning: preg_match_all(): Compilation failed: unrecognized character after
(?< at offset 3 in
/web1/user55305/website/new/libraries/vendor/joomla/application/src/Web/WebClient.php
on line 304
i don't know what to do and the host company does not respond! and i don't really understand php !
I installed the web site on another server and i have not the problem!!what can i ask the host company where the problem appears?
thks for assistance.
Pascal

Hi Pascal,
sorry I dont know anything about this problem.
Please check the rquirements and the php functions and so on....
Requirements
- PHP 5.5+
- PHP Multibyte String support
- PHP JSON support
- PHP DOM XML support

thks for your answer - i will investigate all that.
best regards.
Pascal