I found solution myself. It is: use Win32::OLE::Variant; The part of the code now looks like this:

$userTaxId_var= Variant(VT_VARIANT|VT_BYREF, $userTaxId);
$corpTaxId_var= Variant(VT_VARIANT|VT_BYREF, $corpTaxId);
      my $identified = $identi->IdentifyUserByCert($certificate, $user
+TaxId_var, $corpTaxId_var);
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