Terminal API fundamentals

The Terminal API allows you to make payments, perform refunds, collect shopper information, and other shopper-terminal interactions.

Before you make any point of sale payments, it is important to understand how our Terminal API works and how requests and responses are structured.

Here we describe:

• The endpoints and authentication.
• The API structure.
• Making requests.
• Receiving responses.
• How to receive webhooks.
• How to handle errors.

Endpoints and authentication

The endpoints you need to use, and how you authenticate requests depends on how your integration connects to the Adyen payments platform:

• Local communications.
• Cloud communications.

Local communications

If your integration uses local communications, all your API requests are made from a cash register directly to a terminal's IP address. Alternatively, if you assign a hostname to your terminal, you can make requests to the resolvable hostname of the terminal.

The terminal listens for POST requests to /nexo on port 8443. For example, if your terminal has the IP address 192.168.1.123 you would make API requests to: https://192.168.1.123:8443/nexo

To authenticate your requests, you will need to add Adyen's certificate to your cash register, and encrypt your messages.

Cloud communications

If your integration uses cloud communications, your cash register makes API requests to the Adyen payments platform. Our platform then forwards the request to the terminal.

The endpoint you need to use depends on whether your integration will receive transaction results synchronously or asynchronously:

• Syncronous result: https://terminal-api-test.adyen.com/sync
• Asyncronous result: https://terminal-api-test.adyen.com/async

To authenticate your requests you will need an Adyen API key. If you don't already have an API key you can get one here. You need to include this API key in the header of each Terminal API request.

API structure

Our Terminal API communicates with the terminal using JSON messages. All requests and responses have the following header-body structure:

• Header: Identifies the type of transaction, the terminal being used, and unique transaction identifiers.
• Body: A request or response object, depending on the type of transaction. For example, when you make a payment request this is a PaymentRequest object, and when you receive a payment response this is a PaymentResponse object.

The header and body of Terminal API requests and responses are described in more detail below.

Requests

Each Terminal API request you make is contained in a SaletoPOIRequest object. In this, you need to provide a:

• MessageHeader object.
• Request body object corresponding to the type of transaction. For example, this is a PaymentRequest object when you are making a payment, or an InputRequest object when you are requesting shopper input.

Request MessageHeader

In each request MessageHeader, specify the following:

Name	Required	Type	Description
ProtocolVersion	Yes	String	Version of Adyen's Terminal API. The current version is 3.0
MessageCategory	Yes	Enum	The type of transaction. For example, Payment for a payment request. We will specify which MessageCategory is required throughout our point of sale documentation.
MessageType	Yes	Enum	This is always Request.
MessageClass	Yes	Enum	This is always Service.
SaleID	Yes	String	Your unique ID for your cash register.
ServiceID	Yes	String	Your unique ID for the transaction attempt. This ID needs to be unique within the last 48 hours.
POIID	Yes	String	The unique ID of the terminal, in the format [device model]-[serial number]. For example, P400-123456789. You can find the device model and serial number of a terminal in your Customer Area, under Point of sale > Terminals. The serial number (or s/n) is also printed on the underside of each terminal.
TransactionID	Conditional	String	Your unique reference for the transaction. If you're using Adyen for Online payments, or as a Unified Commerce solution, this is the equivalent of the reference.

The example below shows the header you would provide if you wanted to make a payment.

{
  "SaleToPOIRequest":{
    "MessageHeader":{
      "ProtocolVersion":"3.0",
      "MessageClass":"Service",
      "MessageCategory":"Payment",
      "MessageType":"Request",
      "SaleID":"POSSystemID12345",
      "ServiceID":"0207111104",
      "POIID":"V400m-324688179",
      "TransactionID":"27908"
    },
    "PaymentRequest":{...}
  }
}

Request body

The values you need to include in the request body depends on the type of transaction you are making. We provide examples and reference information for each transaction type throughout our point of sale documentation.

Responses

Each terminal API response you receive is contained in a SaletoPOIResponse object, and includes a:

• MessageHeader object: Echoes the MessageHeader values you provided in the API request.
• Response body object: Corresponds to the type of transaction request you made.
  For example, when you make a PaymentRequest you receive a PaymentResponse object.

Response MessageHeader

The MessageHeader you receive in the response will echo the values you provided in the request. The only exception is the MessageType, which will be Response.

The following example shows the header you would receive in response to the example payment request provided above.

{
  "SaleToPOIResponse":{
    "MessageHeader":{
      "ProtocolVersion":"3.0",                  // Echoed from request
      "MessageClass":"Service",                 // Echoed from request
      "MessageCategory":"Payment",              // Echoed from request
      "MessageType":"Response",                 // Response
      "SaleID":"POSSystemID12345",              // Echoed from request
      "ServiceID":"0207111104",                 // Echoed from request
      "POIID":"V400m-324688179",                // Echoed from request
      "TransactionID":"27908",                  // Echoed from request
    },
    "PaymentResponse":{...}                     // Response body object
  }
}

Response body

The values you receive in the response body depends on the type of transaction request you made. We provide examples and reference information for each transaction type throughout our point of sale documentation.

The response body will often include a unique transaction identifier, and data you can use to generate your receipts.

Transaction identifier

Every API request that creates a transaction or interacts with your money flow (such as a payment or refund) returns a unique transaction identifer in the POITransactionID.TransactionID:

This identifier contains two values, separated by a dot:

• Tender reference: Unique value generated by the terminal for the transaction.
• PSP reference: Unique value generated by the Adyen payments platform for the transaction.

  If you're using Adyen for online payments or Unified Commerce, the PSP reference is the equivalent of the pspReference that you receive for transactions made online.

You should store each transaction identifier you receive, as you will need it to:

• Make a refund.
• Make a payment with acquired card details.
• Identify the transaction in your Customer Area, or in reports generated by Adyen.

Transaction identifiers for offline payments

If your integration uses local communications, your terminals will be able to make Offline EMV and Store & Forward transactions. When you experience a network issue, an Approved payment will only generate a transaction identifier with the tender reference:

Once the terminal is able to connect to the internet again, the Adyen payments platform will process the payment and generate a PSP reference. The PSP reference and tender reference can be found in your Customer Area, and in reports generated by Adyen.

Receipt data

When you make a transaction such as a payment, the payment result contains a PaymentReceipt object. You can add the key-value pairs from this object to the receipt that you print, display, or email to your shopper.

For more information, see our receipts documentation.

Receiving webhooks

As you perform payments and other interactions with your integration, your terminal will generate notifications. These are JSON formatted webhooks that can be sent to endpoints on your cash register, and used to inform your store staff of important events.

There are two types of notifications that can be sent to your cash register:

• Display notifications: Inform your store staff of events that relate to a transaction, such as indicating whether the shopper is interacting with the terminal, or the result of the payment.

  If your integration uses cloud communications with an asynchronous result, you will need to integrate display notifications to receive the result of your transactions.

• Event notifications: Inform your store staff of a terminal's availability and state, including when terminal is beginning maintenance, or shutting down.

In addition to these, Adyen can send platform notifications to your back office server. You can use these to help automate business processes, such as reporting and reconciliation, or to keep your Order Management System (OMS) up to date.

Handling errors

As you integrate, you may receive an error message in the API response. For information on these errors and how to resolve them, see Error scenarios.

If you do not receive a response to an API request, your connection may have dropped after the request was sent. For more information on how to handle this scenario, refer to verifying a transaction status.

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Now that you understand the fundamentals of our Terminal API, you can start making payments.