Thanks again for your reply. Finally I've found what went wrong, the code after A) doesn't work and B) solved my problem:
A) $amount = $_COOKIE["amount"];
B) $amount = $_COOKIE["AMOUNT"];
Although the cookie was set with Cookies Toolkit in lowercase, in PHP it was necessary to get it in UPPERCASE like all other cookies. This was shown with the next code:
<?php
print_r($_COOKIE);
?>
Strange, but it displays an array with all cookie names in uppercase. Anyway my problem was solved and my PHP-skills were trained ;-)
