There are different types of transactions with each transaction type having its own abbreviation in the BIP. 

The below list should help you in making the best decision.

Preauthorization (PA)*

For credit card transactions the payment amount gets additionally reserved (blocked) on the credit card of the shopper. A following Capture (CP) with reference to the Preauthorisation (PA) will trigger the actual settlement of the funds.

Capture (CP)

Captures a preauthorized (PA) amount. Only then this amount will be settled to the merchants bank account.

Debit (DB)**

Debits the account of the shopper and credits the merchant account. This payment type combines a PA and CP into one call, rather than a “dual message” capture of funds.

Refund (RF)**

Credits the account of the shopper with a reference to a prior Debit (DB) or Credit (CD) transaction. The shopper will always see two bookings on his statement. Some connectors don’t support Refunds.

Reversal (RV)*

Reverses an already processed Preauthorization (PA). As a consequence the shopper will never see any booking on his statement. A Reversal is only possible prior to a connector’s specific cut off time for settling transactions. Not all connectors (specifically many virtual account (VA) connectors) support this functionality as their cut off time is at the moment of the transaction occurring.

Credit  (CD)

Credits the account of the shopper and debits the merchant account. - this can at times be used by the PSP

*Please note that Reversal's only work for Pre Authorisation's.

**If a transaction is marked as DB and you would like to return money to the customer then please use the refund option.