# Endpoints (Inbound Calls)
source: https://developer.mastercard.com/transaction-notifications/documentation/api-reference/endpoints/index.md

## Overview {#overview}

The Transaction Notifications API currently exposes two endpoints:

* [Post Transaction](https://developer.mastercard.com/transaction-notifications/documentation/api-reference/endpoints/index.md#post-transaction) to simulate a transaction in Sandbox.
* Get Undelivered Transaction Notifications.

## Security {#security}

### In Short {#in-short}

* Mastercard uses OAuth 1.0a for authenticating client applications.
* Requests with a body must be signed using the Google Request Body Hash extension for OAuth.
* OAuth Keys for your project can be set up in your dashboard.
* Client authentication libraries can be found on GitHub, with how-to information provided in README.md files.

### OAuth Keys \& Authentication Libraries {#oauth-keys--authentication-libraries}

For details please refer to [Using OAuth 1.0a to Access Mastercard APIs](https://developer.mastercard.com/platform/documentation/using-oauth-1a-to-access-mastercard-apis/).

## Environments {#environments}

* Sandbox
* Production

```Sandbox
https://sandbox.api.mastercard.com/openapis/
```

```Production
https://api.mastercard.com/openapis/
```

## OpenAPI Specification {#openapi-specification}


API Specification: `https://static.developer.mastercard.com/content/transaction-notifications/swagger/inbound.yaml`

### Error Codes {#error-codes}

For error codes and error response format, please refer to the [Codes-and-formats](https://developer.mastercard.com/transaction-notifications/documentation/codes-and-formats/index.md) page.

## Post Transaction {#post-transaction}

Warning: This endpoint is limited to **Sandbox** environment.

Transaction Simulation endpoint is used to create a test transaction in the Sandbox environment so you can simulate and test the end-to-end user experience.

### How It Works {#how-it-works}

Diagram usertransactionsimulation

1. Consumer requests to enrol the card

2. You can create card ref using [Consent Management API's](https://developer.mastercard.com/consent-management/documentation/api-reference/#openapi-specification).  

3. You make a call to simulate a purchase using card reference OR card number.  

4. Mastercard forwards the simulated transaction to your defined [Endpoint](https://developer.mastercard.com/transaction-notifications/documentation/api-reference/transaction-notification-webhook/index.md).  
   The notification contains the card reference, amount, merchant details and the issuer decision (approval/decline - similar to the real-time notification you will receive in production environment). For a full list of data elements please check the [Outbound Calls](https://developer.mastercard.com/transaction-notifications/documentation/api-reference/transaction-notification-webhook/index.md#openapi-specification).

5. You receive the simulated notification containing the card reference and associate it to your user.

6. You may optionally perform a communication to the cardholder by notifying the cardholder of an offer or any other type of communication.