I have error in debug.log year:
Notice: Undefined index: redirect_active in /var/www/html/oc-content/plugins/advertisement_manager/index.php on line 370
Line 370 is:
if ($ _ GET [ 'redirect_active'] == 1 and $ _GET [ 'url_go'] <> '' and $ _GET [ 'campaign'] <> '') {

Why shouldnt I change?
Thank you

@Dan Dan
It is only notice, you should disable them in production website.
Anyway you can fix it by rewritting code:
if ($ _ GET [ 'redirect_active'] == 1 and $ _GET [ 'url_go'] <> '' and $ _GET [ 'campaign'] <> '') {
into:
if (isset($_GET [ 'redirect_active']) && isset($_GET [ 'url_go']) && isset($_GET [ 'campaign']) && $_GET [ 'redirect_active'] == 1 and $_GET [ 'url_go'] <> '' and $_GET [ 'campaign'] <> '') {

Thank you. Problem solved

@Dan Dan
Great