I must print the cookie into the h....and for the html to work correctly I need

Kindly go back to the manuals I linked :)

You can only print the header once, and once only, this is the rule of HTTP, no way around it

Instead of broken logic

if ( blah ){
    print header( and cookie );
}
print header;
[download]

use correct logic for print headers only once

if ( blah ){
   store cookie in variable
}
print header ( and $cookie )
[download]