# Enroll User
source: https://developer.mastercard.com/priceless-planet-carbon-tracker/documentation/use-cases/enroll_user/index.md

## Overview {#overview}

The `POST /issuers/users` endpoint registers cardholders on the Carbon Calculator Experience (CCE) platform. The CCE service provides the **Donate** toggle, which allows the issuers to enable or disable the Donation feature during onboarding.

If the issuer has opted for the Donation feature, these fields are mandatory in the payload:

* name
* billing address
* email
* locale
* cardholder name
* card number
* card base currency
* card expiration date  

Once you enroll a user on the CCE platform, the transactions from the last 12 months are scored for their carbon footprint. This process usually takes 24 hours to complete from the enrollment.
Note: If you toggle ON the Donate feature after it was initially OFF during enrollment, all current CCE users must go through the registration process again to continue using the platform seamlessly.

## Pre-requisites {#pre-requisites}

* Read and understand the [Payload Encryption](https://developer.mastercard.com/platform/documentation/security-and-authentication/securing-sensitive-data-using-payload-encryption/) guide for secure data communication with the API.
* Refer to the [Mastercard Encryption](https://developer.mastercard.com/platform/documentation/security-and-authentication/securing-sensitive-data-using-payload-encryption/#mastercard-encryption) topic to know how to encrypt and decrypt the Carbon Calculator Experience API payloads.

Tip: To create your project on Mastercard Developers, refer to the [Quick Start Guide](https://developer.mastercard.com/priceless-planet-carbon-tracker/documentation/quick-start-guide/index.md) for more information.

## Sequence Diagram {#sequence-diagram}

The following sequence diagram shows the order of events for a solution that uses the `POST /issuers/users` endpoint.
Diagram enroll_user

## Execution Steps {#execution-steps}

The following details the steps in the above sequence diagram:

1. The consumer sends the request for enrollment on the Carbon Calculator Experience platform.
2. The issuer app sends the consumer enrollment request to the issuer server.
3. The issuer server sends the consumer enrollment request to the `POST /issuers/users` endpoint.
4. The Carbon Calculator Experience application validates the request for data format, duplicate PAN check, and BIN validation.
5. The application performs the enrollment and persists the new user data.
6. The application returns the user ID along with other user information to the issuer server.
7. The issuer server stores the user ID and sends it back to the issuer app if required.
8. (Optional) The issuer app displays the successful registration confirmation to the consumer.

## Error Messages {#error-messages}

You receive an error response for an invalid request or any missing request parameter.   

For more information about the error codes, refer to the [Code and Formats](https://developer.mastercard.com/priceless-planet-carbon-tracker/documentation/code-and-formats/index.md) section.

## Endpoint {#endpoint}


API Reference: `GET /issuers/users`

## Sample Request and Response {#sample-request-and-response}

For more details on the sample request and response, refer to the [How to call the Enroll User API](https://developer.mastercard.com/priceless-planet-carbon-tracker/tutorial/test-cases/step1/index.md) tutorial.