In your store's Admin area, go to the Extensions > Payments > Authorize.Net
Status: - MUST be "ON" for Payment module to appear in your store.
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Transaction Mode: - Select whether or not the Orders placed using this payment method will be test Orders. Before you take your site live you will want to make sure you set this drop-down to Test.
Transaction Method: - Authorize.net is an on-line payment method. Therefore, the credit card must be Authorized by the payment gateway when the order is submitted, in order for it to complete. However, you can choose whether you want to Authorize Only, or Capture the payment simultaneously during the Order creation. If you choose to Capture, an Invoice will automatically be created for the full quantity of items in the Order.
Order Status: - Select the Order Status of all new Orders created using this payment method from the drop-down. The recommended status is Pending, as this is intended to apply to Orders which have not had any actions performed on them, however you can change this to whichever status you prefer.
Decline attempts limit: Security setting to prevent fraud attacks. If number of sequential declines exceed the limit, customer's account will be locked and message sent to administrator.