Install and run the local service and make the requests to it.
The base URL for all requests is:
https://blockchain.info/merchant/$guid/ "
https://localhost:3000/merchant/$guid" where $guid is your Blockchain Wallet ID (used to login), and you should use the parameter "?password=
main_password" where main_password is your wallet password.
Here is an example for PHP:
<?
$guid="GUID_HERE"; // YOUR WALLET ID
$firstpassword="PASSWORD_HERE"; // YOUR PASSWORD
$secondpassword="PASSWORD_HERE"; // SECOND PASSWORD IF YOUR ACCOUNT HAS DOUBLE ENCRYPTION ENABLED
$amounta = "10000000";
$amountb = "400000";
$addressa = "1A8JiWcwvpY7tAopUkSnGuEYHmzGYfZPiq";
$addressb = "1ExD2je6UNxL5oSu6iPUhn9Ta7UrN8bjBy";
$recipients = urlencode('{
"'.$addressa.'": '.$amounta.',
"'.$addressb.'": '.$amountb.'
}');
$json_url = "http://localhost:3000/merchant/$guid/sendmany?password=$firstpassword&second_password=$secondpassword&recipients=$recipients";
$json_data = file_get_contents($json_url);
$json_feed = json_decode($json_data);
$message = $json_feed->message;
$txid = $json_feed->tx_hash;
?>
Source:
https://www.blockchain.com/pt/api/blockchain_wallet_api