Edit History

I lied, it doesn't work, sorry for the spam.

So if somebody (a real person) could help, it would be really appreciated.

Ok, Thanks to ChatGPT (yeah its real), i've found a solution.

After discussing with him about the ps8moduly.cz 's code, and after he tell me that i should do it with override(i know), he tell me that the main reason for this error should be "Session Initialization : the session might not be fully initialized or updated during the very first visit to a new cart. This could potentially affect the behavior of the code". 

So i asked him how to repair that. 
He tell me to add this below code before the ps8moduly.cz 's code : 
   // Make sure the session is started and initialized
            if (session_status() !== PHP_SESSION_ACTIVE) {
                session_start();
            }

And it work. (I'm still testing every checkout process, but i've seen no problem for now.)
So thanks to ChatGPT and @ps8moduly.cz, this thread is [SOLVED], thanks !

Ok, Thanks to ChatGPT (yeah its real), i've found a solution.

After discussing with him about the ps8moduly.cz 's code, and after he tell me that i should do it with override(i know), he tell me that the main reason for this error should be "Session Initialization : the session might not be fully initialized or updated during the very first visit to a new cart. This could potentially affect the behavior of the code". 

So i asked him how to repair that. 
He tell me to add this below code before the ps8moduly.cz 's code : 
   // Make sure the session is started and initialized
            if (session_status() !== PHP_SESSION_ACTIVE) {
                session_start();
            }

And it work. (I'm still testing every checkout process, but i've seen no problem for now.)
So thanks to ChatGPT and @ps8moduly.cz, this thread is [SOLVED], thanks !