OK, thanks for @retr0w 's hints , take a deep breath, and clam down.
i was almost there
find out a different size of response body, right click and open in Editor , then i found the flag.
anyway , i hate ZAP , i prefer ffuf
This really helped me! I combined it with another comment I saw here as well to get the answer… When sending a request think about the method GET vs. POST.
Thanks for all the help!
This helped me, to use POST Method
Use Cookie: cookie=something and select the value (in my case it’s something) then add the payload and processor.
The ideea is that the response will have a larger body size due to the presence of the flag.
It’s actually simpler than we are used to think.
it’s good to have a alternative to ZAP Fuzzer, heres one you can do the same task with Burp Suite check it out.
Hello everyone, I wanted to ask you if you consider it necessary to study zap in depth or better dedicate time to burpsuite, which even has a certification 
.