Apollo has now integrated with Authorize.net. Just few steps configuration and you are all set.
Once you have signed with Authorize.net login into Authorize.net
Then click on settings:
Click on the "API Credentials and keys" link:
Note down the API login key and create new key by clicking on the "New Transaction Key". Note down the newly generated key:
Login into Apollo and navigate to Settings >> Account Setup:
Go to the "Payment gateway information for online credit card processing" section. Select Authorize.net and enter the API login key and transaction key noted in the earlier step and click Save. Now your payment is integrated with Authorize.net: