I have just setup list subscribe using php and MCAPI examples and all seems to be working well besides the update_existing.
if($_POST['submit']) {
require_once 'MCAPI.class.php';
$apikey = 'mykey';
$listId = 'mylist';
$my_email = $_POST['email'];
$merge_vars = Array('FNAME' => $_POST['first_name'], 'LNAME' => $_POST['last_name'] );
$double_optin = false;
$update_existing = true;
$send_welcome = false;
$api = new MCAPI($apikey);
$retval = $api->listSubscribe( $listId, $my_email, $merge_vars, $double_optin, $update_existing,$send_welcome); {
if ($api->errorCode){
echo "Unable to load listSubscribe()!\n";
echo "\tCode=".$api->errorCode."\n";
echo "\tMsg=".$api->errorMessage."\n";
} else {
echo "Subscribed - look for the confirmation email!\n";
}
}
}