Authorize.net Users:

If your organization uses Authorize.net, sign up for the Automated Recurring Billing™ (ARB) service by following the steps below:

1. Log in to your Merchant Interface at https://account.authorize.net.
2. Click Merchant Profile in the main left side menu.  
3. Click Sign Up next to Automated Recurring Billing. The Automated Recurring Billing Service Addendum page appears.
4. Click the check box labeled I have read and understand the Terms of Service.
5. Click I Agree.

Important: Add a Silent Post URL:
    1. Log in to your Merchant Interface at https://account.authorize.net.
    2. Click Settings in the main left side menu.
    3. Click Silent Post URL.
    4. In the URL text field, enter the URL to which the payment gateway should copy the transaction relay response. This URL must be "https://www.givezooks.com/authorize/ipn"
    5. Click Submit. A confirmation message indicates that the URL has been added.
 

Link to Authorize.net's support site.

Authorize.net phone support 877-447-3938.