The various services used to process payments are at the heart of payment processing. These services enable customers to purchase goods and services, merchants receive payments from the customer's accounts, merchants to provide refunds, and merchants to void transactions.

Authorizations

An authorization confirms that a payment card account includes enough funds to pay for a purchase. Authorizations fall into two categories: online and offline.

Offline Authorizations

Online transactions require an internet connection. In situations where the internet is not available, for example, due to an outage, merchants can continue to take credit card payments using offline transactions. An offline authorization is an authorization request for which you do not receive an immediate confirmation about the availability of funds.
Offline authorizations have a higher level of risk than online transactions because they do not provide fund availability confirmations or set aside the funds for later capture. Further, it can take up to five days to receive payment confirmations for offline transactions. To mitigate this risk, you can choose to only fulfill orders after receiving payment confirmations.

Sales

A sale is a bundled authorization and capture. Some processors and acquirers require a sale transaction instead of using separate authorization and capture requests. For other processors and acquirers, you can request a sale instead of a separate authorization and capture when you provide the goods or services immediately after taking an order.
There are two types of sale processing: Dual-Message Processing and Single-Message Processing.