my  $request = HTTP::Request::Common::POST( BOX,  
    [
    Content_Type => 'form-data',
    Authorization => "Bearer $token",
    Content => [ 
        attributes => $c,                #encoded json
        file       => [ "$Bin/test.txt" ],    #file_path
        ],
    ]
);
[download]

 sub build_json_request {
    my ($url) = @_;
    my $header = ['Authorization' => "Bearer $token", 'Content-Type' =
+> 'form-data'];
    return HTTP::Request->new('POST', $url, $header, {attributes => $c
+, file=> [ "$Bin/upload.bak" ],} );
}

my $r = build_json_request (ENDPOINT );
my $res = $ua->request($r);
[download]

not sure if LWP::Useragent will fetch the file contain itself

Yes, it will. Try

#!/usr/bin/perl
use strict;
use warnings;
use LWP::UserAgent;
use JSON;
use FindBin qw($Bin);;

my $token = '';
my $url   = 'http://';
my $attributes = encode_json ({ 
   name => "test.txt", 
   parent => { id => 0 }
});

my $ua  = LWP::UserAgent->new;
my $response = $ua->post($url,
   Content_Type => 'form-data',
   Authorization => "Bearer $token",
   Content => [
      attributes => $attributes,
      file       => [ "$Bin/test.txt" ],
   ],
);

if ($response->is_success) {
  print $response->decoded_content; 
} else {
  die $response->status_line;
}
[download]

poj

OMG it works like charm. I still dont know why I was complicating the things. This code block works perfectly for me. Thanks you so much @poj I got stuck for like couple of days on this issue. Now I am good to go ahead its part of CPAN module I am creating. once again thanks for your help.