thanks to poj who helped me on this 400 BAD REQUEST to structure the request. then I came up with header structure and body structure. now am trying to make the request but am getting 500 Not a SCALAR reference

    #!/usr/bin/perl 

    use strict;
    use warnings;
    use HTTP::Request::Common qw(POST);
    use LWP::UserAgent;
    use Digest::SHA qw(hmac_sha256_hex);
    use URI;
    use Encode;
    use HTTP::Headers;
    use HTTP::Message;
    
    my $nonce = 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/^[?]//;
    printf "params = %s\n", $post_params_urlencoded;                  
    
    my $message = encode('utf8',$nonce.$hmac_key.$api_endpoint.$post_p
+arams_urlencoded);
    my $signature =  uc hmac_sha256_hex($message, $hmac_secret);
    printf "sig = %s\n",$signature;
    
    print"\n";
    
    print "headers are:\n";
    
    my $headers = HTTP::Headers->new(
            'Apiauth-Key'           =>  $hmac_key,
            'Apiauth-Nonce'         =>  $nonce,
            'Apiauth-Signature'     =>  $signature,
        );
    
    
    my $body = HTTP::Message->new($headers, $post_params_urlencoded);
    print $body->as_string;
    
    my $ua = LWP::UserAgent->new;
    $ua->agent("MyApp/0.1 ");
    
    my $req = HTTP::Request->new(POST => $url);
    $req->content($body);
    my $res = $ua->request($req);
    
    print "Content-type: text/plain\n\n";
    if ($res->is_success) {
       print $res->content;
    }
    else {
       print $res->status_line, "\n";
    }
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Output

params = currency=USD&amount=500&internal=0&description=HEY
sig = FE5B4A4A66FEAB0C1216B59C81BC2FD2CA5DC4459D84CF9A7DD8EFE37242E59A

headers are:
Apiauth-Key: sdfsdfdsfdsfy
Apiauth-Nonce: 1000
Apiauth-Signature: FE5B4A4A66FEAB0C1216B59C81BC2FD2CA5DC4459D84CF9A7DD
+8EFE37242E
59A

currency=USD&amount=500&internal=0&description=HEY
Content-type: text/plain

500 Not a SCALAR reference
Press any key to continue . . .
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