Standard (non-recurring) transactions can use either Capture or Authorise payment methods.
Capture charges the customer’s credit card immediately. This is the default payment method, and is the method most websites will use for credit card payments.
Authorise checks to see that the transaction would be approved, but does not process it. Eway calls this method PreAuth (or Stored Payments in the old XML API). Once the transaction has been authorised, you can complete it manually in your MYEway console. You cannot complete PreAuth transactions from WordPress/Gravity Forms.
Free add-on: you need to add your Eway API key and password to see PreAuth transactions in the sandbox, so that the Rapid API is used. The old Stored Payments XML API does not have a sandbox.
NB: PreAuth is currently only available for Australian, Singapore, Malaysian, & Hong Kong merchants. Do not select Authorise if you are a New Zealand merchant!