If you have configured the registration module for recurring billing and a user completes the registration they will see the following message displayed:
Payment Status: Ok
Transaction #: 33454221
The message above indicates that the recurring transaction was submitted successfully. After a successful registration, the module sends the recurring billing transaction to the payment gateway and Authorize.Net creates a recurring billing transaction (ARB) on their servert. ARB transactions are authorized around midnight in your timezone so you wont see the credit card authorization in the standard reports right away at auth.net until tomorrow. If you log into your auth.net virtual terminal and run the report to show your ARB subscriptions setup you will see the transaction there.