The createCustomer() method takes a CreateCustomerRequest object as its only parameter. This parameter is optional.
$request = $stripe->customers->createCustomerRequest()->setAccountBalance(-500);
$stripe->customers->createCustomer($request);
$customer = $stripe->customers->getCustomer("customer_id");
The UpdateCustomer() method takes an UpdateCustomerRequest object as its second parameter.
$request = $stripe->customers->updateCustomerRequest()->setEmail("foo@bar.com");
$stripe->customers->updateCustomer("customer_id", $request);
$stripe->customers->deleteCustomer("customer_id");
$customers = $stripe->customers->listCustomers();