Warning note after installation

Hi everybody,
I’ve choose a Leanex Lite theme for a website but as I’ve installed it,
is appeared this note:
Warning: Use of undefined constant LEANEX_LITE_PREMIUM – assumed ‘LEANEX_LITE_PREMIUM’ (this will throw an Error in a future version of PHP) in /web/htdocs/…/home/wp-content/themes/leanex-lite/inc/admin/theme-get-started.php on line 106
Could someone help me to understand what does it mean and what should I do?
Thanks in advance!