I am not getting that error either, but are you sure that is your exact script - e.g. if you print the number before encoding it becomes a string. You can numify it by adding 0:

my $json = {
    'book' => {
        'title' => JSON::PP::true,
        'pages' => 5.03
    }
};

print $json->{'book'}{'pages'}, "\n";
my $string = encode_json($json);
print "After printing: $string\n";

$json->{'book'}{'pages'} += 0;
my $string2 = encode_json($json);
print "After numify: $string2\n";
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Output:

5.03
After printing: {"book":{"title":true,"pages":"5.03"}}
After numify: {"book":{"title":true,"pages":5.03}}
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