Php MongoDB异常：未授权db执行命令{update：

I have the following code

$bulkWrite=new MongoDB\Driver\BulkWrite;
$filter = ['name' => 'John'];
$update = ['$set' => ['name' => 'Smith', age: 35, profession => 'pilot']];
$options = array('multi' => false, 'upsert' => false);
$bulkWrite->update($filter, $options);
$mongoConn->executeBulkWrite('MyCollection', $bulkWrite);

The code returns the error:

Exception:not authorized on db to execute command { update:

What is the issue?

After reviewing the code I found that the issue is in the name of the collection.
If we have before:

$DB_CONNECTION_STRING="mongodb://dbName:dbPassword";
require '../../vendor/autoload.php';
$mongoConn = new MongoDB\Driver\Manager( $DB_CONNECTION_STRING );

Then after we need to have the correct reference to the dbName:

$bulkWrite=new MongoDB\Driver\BulkWrite;
$filter = ['name' => 'John'];
$update = ['$set' => ['name' => 'Smith', age: 35, profession => 'pilot']];
$options = array('multi' => false, 'upsert' => false);
$bulkWrite->update($filter, $options);
$mongoConn->executeBulkWrite('dbName.MyCollection', $bulkWrite);