->add_string does not take an array as its first parameter, and it is documented to only take one or two parameters overall. As your array @ar contains two elements, your call is equivalent to

 my @ar = ("82.94.229.0/24", "81.52.140.0/24");
 $pt->add_string("82.94.229.0/24", "81.52.140.0/24", "82.94.229.0/24 8
+1.52.140.0/24");
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I don't know what this means to Net::Patricia, but you will either need to read the documentation for Net::Patricia closer or learn more about Perl and how it flattens lists.