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

use Digest::SHA qw(sha256 sha256_hex);

my $digest=sha256_hex("138539083512345apiKeyDEMO","apiSecretDEMO" );
print "Digest=$digest\n";

# correct answer is:
#696E087F4B1902AA58D35E75B4600580D70A92ED68B23379373117FB3FE3064A

# my code generates:
#ea645ae07e04289f3fe14c81af54f7da9cae1114fe2bb9efbb6b383ef276434b