According to the documentation, this should work (and if I understand the output, it really does).

#!/usr/bin/perl
use warnings;
use strict;

use LWP::UserAgent;
use Cpanel::JSON::XS qw{ encode_json };

my $ua = 'LWP::UserAgent'->new(timeout => 1);
my $response = $ua->post('https://httpbin.org/post',
                         'content-type' => 'application/json',
                         Content => encode_json({key => 'value'}));

print $response->decoded_content;
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