# Transactions source: https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/transaction/index.md Transactions are actions that are made on the order. They might be authenticating the payer or card, reserving payer funds, or moving money between you and the payer. You initiate a transaction in your system by sending an API request to the Mastercard Gateway, which in turn processes the request and sends it forward to a relevant payment method provider or acquirer. To perform any API operation, such as initiate a transaction, you must have the required privilege set on your merchant profile with the gateway. To check which transactions you can initiate, contact your payment service provider. Non-card payments or debit networks may have a limited set of API operations when compared to credit cards. The sections describe the use cases for individual card transactions. They include simple request examples with the mandatory fields only, using a credit card payment method with stored credit card details provided as a token. For more request and response examples, see the [Postman collection](https://www.postman.com/mastercard/mastercard-developers/collection/4fakvrd/mastercard-gateway-api). Alert: The operations available to you are limited by the capability of the acquirers configured on your merchant profile. If the acquirer does not support an operation or its privilege is not configured on your profile, all your requests for that operation for that specific acquirer are rejected.
## Initial, standalone, and subsequent transactions {#initial-standalone-and-subsequent-transactions} The transactions supported in the Mastercard Gateway are divided into four groups, based on how they can be used. * Initial The initial transactions create a new order and start the payment flow for the sale instance. These transactions need a unique order ID that defines the new order. The transaction types can be used as initial transactions: * [INITIATE_AUTHENTICATION](https://developer.mastercard.com/mastercard-gateway/documentation/api-reference/v100/rest/api-ops/index.md#authentication) * [AUTHORIZE](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md) * [DISBURSEMENT](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md#disbursement) * [PAY](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md#pay) * [VERIFY](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md#verify) * Standalone The standalone transactions are a special type of initial transaction, used in a situation where the initial transaction for an order is performed outside the gateway or you simply do not want to associate the transaction with an existing order. These transactions are also known in the industry as unreferenced, unmatched, or unlinked transactions and are not enabled by default due to risk of fraud. The transaction types can be used as standalone transactions: * [STANDALONE CAPTURE](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md#standalone-capture) * [STANDALONE REFUND](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md#standalone-refund) * Subsequent The subsequent transactions are related to an existing order, as they modify or progress that order in some way. These transactions must link to an initial transaction using its order ID. The transaction types can be used as subsequent transactions: * [AUTHENTICATE PAYER](https://developer.mastercard.com/mastercard-gateway/documentation/api-reference/v100/rest/api-ops/index.md#authentication) * [AUTHORIZE](https://developer.mastercard.com/mastercard-gateway/documentation/api-reference/v100/rest/api-ops/index.md#authentication) * [CAPTURE](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md#capture) * [DISBURSEMENT](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md#disbursement) * [PAY](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md#pay) * [REFERRAL](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md#referral) * [REFUND](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md#refund) * [UPDATE AUTHORIZATION](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md#update-authorization) * [VOID](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md#void) * [CHARGEBACK](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md#chargeback) * Informational To provide additional information regarding the order, the payment processor or acquirer creates the informational transactions. Warning: The AUTHORIZE, DISBURSEMENT, PAY, EMV 3-D Secure operations, and VERIFY transactions can be both initial and subsequent. All integration methods and payment methods do not support all transaction types. For the exact types available for your setup, check out the details for the integration and payment methods you want to use from [Choosing an Integration Method](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/choosing-int-method/index.md) and [Payment Methods](https://developer.mastercard.com/mastercard-gateway/documentation/payment-methods/index.md). For more information about Authorize, see [Authorize](https://developer.mastercard.com/mastercard-gateway/documentation/getting-started/order-trans-concepts/authorize/index.md).