To setup recurring billing on the Authorize.Net payment form you can configure a new field on the authorize.net payment form called Recurring Billing Transaction which indicates whether the transaction is a recurring billing transaction.
To configure additional fields that you would like to appear on your payment form follow these steps:
1. Log into the Merchant Interface at https://secure.authorize.net
2. Click Settings under Account in the main menu on the left
3. Click Payment Form in the Transaction Format Settings section
4. Click Form Fields
5. Click to select the checkbox(s) in the View column next to the fields you would like to display on your payment form
6. For each field you are adding, click to select the check boxes in the Edit and Required columns if you would also like to configure either or both of these attributes for the field
a. View – The customer can view but not edit the information. For example, if you would like to display an invoice number. Information that is View only should be submitted with the transaction information to the payment gateway. Contact your Web developer for more information.
b. Edit – The customer can view and/or edit the information but the field is not required to submit the transaction. For example, if you would like to collect but not require the customer’s email address, configuring the field as View and Edit allows the customer to provide this information with the transaction.
c. Required – The customer must provide the information in order to submit the transaction. For example, if you would like to require the customer's card code. When requiring this field, the View, Edit and Required attributes must be configured.
7. Click Submit
Be sure to test your payment form anytime you update fields and their attributes to be sure that it meets your requirements.
See the following url at Authorize.Net for more info on configuring your payment form
http://www.authorize.net/support/merchant/
Navigate to section Form Settings and Customizing the Hosted Payment Form.