1.) Create an account and login to https://www.authorize.net/ ( or https://sandbox.authorize.net/ for test environment )

2.) Go to “Account > API Credentials & Keys” section

3.) Save the “API ID” for provided field, then, fill in the question to obtain new “Transaction Key”

4.) You can check the authorize test card here. https://developer.authorize.net/hello_world/testing_guide/