i have been able to make this API to work, and am successfully interacting with it now

Am trying to make a post with this data

my $url_query = "currency=usdt"."&amount=20"."&address=0x55Dc816924e33
+CA50830A"."&destination_tag=None";
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but am getting this error

{"status": "error", "reason": {"amount": ["This field is required."]}}
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Full code

#!/usr/bin/perl

use strict;
use warnings;
use LWP::UserAgent;
use Digest::SHA qw(hmac_sha256_hex);
use UUID::Tiny ':std';
use URI::Escape;
use JSON;
use Time::HiRes qw(time);
use JSON::XS;



sub write_call_back {
    my ($data, $userp) = @_;
    ${$userp} .= $data;
    return length($data);
}

sub url_encode {
    my ($data) = @_;
    return uri_escape($data);
}

my $api_key = "api_key";
my $api_secret = "api_secret";

my $timestamp = int(time() * 1000);

my $nonce = create_uuid_as_string(UUID_V4);

my $x_auth = "BITSTAMP $api_key";
my $x_auth_nonce = $nonce;
my $x_auth_timestamp = $timestamp;
my $x_auth_version = "v2";
my $content_type = "application/x-www-form-urlencoded";
my $payload = url_encode('{"offset":1}');

my $http_method = "POST";
my $url_host = "www.bitstamp.net";
my $url_path = "/api/v2/usdt_withdrawal/?";
my $url_query = "currency=usdt"."&amount=20"."&address=0x55Dc816924e33
+CA50830A"."&destination_tag=None";

my $data_to_sign = join('', 
    $x_auth, $http_method, $url_host, $url_path, $url_query,
    $content_type, $x_auth_nonce, $x_auth_timestamp, $x_auth_version, 
+$payload
);


my $x_auth_signature = hmac_sha256_hex($data_to_sign, $api_secret);


my $ua = LWP::UserAgent->new;

my $url = "https://$url_host$url_path$url_query";

my $req = HTTP::Request->new(POST => $url);
$req->header('X-Auth' => $x_auth);
$req->header('X-Auth-Signature' => $x_auth_signature);
$req->header('X-Auth-Nonce' => $x_auth_nonce);
$req->header('X-Auth-Timestamp' => $x_auth_timestamp);
$req->header('X-Auth-Version' => $x_auth_version);
$req->header('Content-Type' => $content_type);
$req->content($payload);

my $resp = $ua->request($req);

if ($resp->is_success) {
    print $resp->content;
} else {
    print "HTTP POST error code: ", $resp->code, "\n";
    print "HTTP POST error message: ", $resp->message, "\n";
}
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