To setup Authorize.net Payment gateway, go to Classified Listing=> Settings => Payment=> Authorize.net Cards Settings
If you want to use Authorize.net payment, you first need to enable it by checking the box, and then fill the necessary fields as shown in the window below.
3.3.1) Enable: To enable Authorize.net payment check the “Enable Authorize.net” box.
3.3.2) Title: Give the title that will show as the payment name during checkout process.
3.3.3) Description: Write the description that will be displayed during checkout process.
3.3.4) API Login ID & Transaction Key: Enter the Authorize.net API login ID & Transaction key to complete the payment setup.
3.3.5) Sandbox: Enable Sandbox mode to test whether the payment gateway is successfully activated.
33.8) Select Card: Select the cards that you want to accept.