use strict;
use warnings;

use JSON::PP;

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

open my $fh, '>', 'data_out.json';
print $fh encode_json($json); #this line is in error
close $fh;

##</code><code>##

use strict;
use warnings;

#convert all constant numbers to objects 
#it converted 5.03 to an object and it caused the error
use bignum; 

use JSON::PP;

# some code where "bignum" is used
# ...

no bignum; # exclude bignum usage 
my $json = {
        'book' => {
            'title' => JSON::PP::true,
            'pages' => 5.03 #this number
        }
    };

open my $fh, '>', 'data_out.json';
print $fh encode_json($json); #this line is in error
close $fh;