Setup within Kartris | Kartris User Guide

Go to Configuration > Payment and Shipping Gateways and click to edit AuthorizeNet SIM.
For the 'friendly name', enter the name you want this payment system to be referred to on the front of your site where customers select it, for example 'Pay by credit card with AuthorizeNet'.
Change the status from 'OFF' to 'ON' (for live orders) or 'TEST' or 'FAKE' for testing. 'TEST' means that a test order will be passed, allowing you to test the full integration and pass multiple orders and no cost without needed to do refunds. 'FAKE' means that Kartris will skip the AuthorizeNet payment process and instead format a post back itself to the callback page of Kartris. This is useful for testing that the callback process works, triggers the appropriate emails and so on without keep having to keep going through the test payment process.
ProcessCurrency - Typically AuthorizeNet accounts are single-currency, so you should enter this as a three-letter ISO code, for example 'USD'.
Test URL - (for test orders) should be:
https://test.authorize.net/gateway/transact.dll
Post URL - (for live orders) should be:
https://secure.authorize.net/gateway/transact.dll
TransactionKey - This is the transaction key which is generated on the AuthorizeNet back end system. It is used in the generation of the MD5 hash. If this does not match the one on the back end of AuthorizeNet, transactions will not be accepted by AuthorizeNet.
LoginID - Should be provided to you with your AuthorizeNet account details