To set up Authorize.Net credit card payment integration, the following steps must be followed:
Go to My Account > My Profile and click on the "Permissions" tab
Scroll down and change the Payments field to "write" access, then click on the "Update Permissions" button
Go to Configurations > Payment Methods > + New Payment Method
Select "Authorize.Net" and name the payment method then click "Save"
you will be required to enter the API Login ID and the Transaction Key - you can get these from Authorize.Net (See Below)
Log into your Authorize.Net account and go to "Settings"
Then select API Credentials & Keys
You can take the information from here
Payment can now be taken for an "Approved" transaction by taking the following steps
Enter credit card information and click on "Apply Payment" and the payment will be taken from the customer and applied to the invoice