Step-1: Keep the API Login ID and Transaction Key handy. You will find this on your Authorize .NET Account.
Step-3: Login into Salesforce and search for Event Payment Methods on the App Launcher the click on New Button.
Step-4: Please fill in the required details carefully and Save.
Step-5: Once the Payment Method is Created.
Go to Event Builder → Event Info Menu → Payment Information → EVA Payment Method, Search for the created Payment Method name then select and Save.