If you have custom function that wants to subscribe user in Arigato PRO or Arigato Lite mailing list, here is the code that you need to use.

For Arigato PRO:

if(!class_exists('BFTProUser')) return false; // avoid fatal errors in case Arigato PRO is not activated

$_user = new BFTProUser();
$_user->ignore_redirect = true;

// array with user data:
$vars = array(
"name" => "John Smith", // required
"email" => "john@my-domain.com", // required
"list_id" => 5, // the ID of the mailing list, required
"source" => "my custom function", // optional
);

try {
   // the function returns the newly inserted subscriber ID
   $message = '';
   $subscriber_id = $_user -> subscribe($vars, $message, true);
}
catch(Exception $e) {
   echo $e->getMessage();
}

Essentially this is all you need. The function will ignore list redirect and captcha requirements.

For Arigato Lite:

This is even simpler:

if(!function_exists('bft_subscribe')) return false;
bft_subscribe("john@my-domain.com", "John Smith", true, true);