my %ssh_options = (
  StrictHostKeyChecking => "no"
);

my %args = (
  username  => $user,
  password  => $pass,
  debug     => 1,
  ssh_args  => (options => \%ssh_options)
); 

my $sftp = Net::SFTP->new($host, %args)

##</code><code>##

my %args = (
  username  => $user,
  password  => $pass,
  debug     => 1,
  ssh_args  => (options => { StrictHostKeyChecking => "no"} )
 );