As well, it should be noted that the receipt page and response details do not need to be completed. As part of the payment protocol OPS-COM supplies this information to Authorize.Net
Please be aware your Authorize.net merchant account needs to have the following settings:
Product Type: Card Not Present (CNP)
Market Type: eCommerce
These settings are usually setup by your Authorize.net contact on the initial account creation. If you want to confirm the correct settings go to Account > Merchant Profile. Under the Business Information heading it will show your product and market type.
API credentials are required for communication between OPS-COM and Authorize.Net. You will need 3 pieces of unique identification, one of which (API Login ID) is defined at the time of the account creation.