Why is the Shipping Address not appearing in the Authorize.net payment integration option?

I have clicked the option to add shipping address if different than billing

that option does not appear on the form.

Please note that you will first need to enter the Authorize.net API Login ID and Transaction key. 

Once that is done, you can configure the Additional Gateway Settings, which also includes the Shipping address option.

Please note that you will need to select "Continue" at the bottom of the payment wizard.

Please see the screencast below.