See post

#!/usr/bin/perl 
use strict;
use warnings;
use LWP::UserAgent;
use Digest::SHA qw(hmac_sha256_hex);
use Time::HiRes qw(gettimeofday);
use URI;
use Encode;

my $nonce = int (gettimeofday * 1000);
my $url          = "https://localbitcoins.com";
my $api_endpoint = "/api/merchant/new_invoice/";
my $hmac_key     = "sdfsdfdsfdsfy";
my $hmac_secret  = "sdfdsfdsf";

my %params = (
  currency    => 'USD', amount   => '500', 
  description => 'HEY', internal =>  '0',   
);

my $uri = URI->new();
$uri->query_form( \%params );
my $post_params_urlencoded = $uri->as_string;
$post_params_urlencoded =~ s/^[?]//;

my $message = encode('utf8',$nonce.$hmac_key.$api_endpoint.$post_param
+s_urlencoded);
my $signature =  uc hmac_sha256_hex($message, $hmac_secret);

my %headers = (
  'Apiauth-Key'       =>  $hmac_key,
  'Apiauth-Nonce'     =>  $nonce,
  'Apiauth-Signature' =>  $signature,
);

my $ua = LWP::UserAgent->new;
$ua->agent("MyApp/0.1 ");

# remove exit to send request
$ua->add_handler( 
  request_prepare => sub { 
    print "Request:\n".$_[0]->as_string; exit 
  });

my $res = $ua->post( $url.$api_endpoint, %headers, Content => $post_pa
+rams_urlencoded );
print "Content-type: text/plain\n\n";
if ($res->is_success) {
  print $res->content;
} else {
  print $res->status_line;
}
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