# Testing
source: https://developer.mastercard.com/masterpass-merchant-integration-v7/documentation/testing/index.md

## Masterpass Sandbox Testing {#masterpass-sandbox-testing}

To test in the Masterpass sandbox environment, you will need to [sign up](http://sandbox.masterpass.com/) for a Masterpass sandbox wallet account.

For further details, see [Sandbox Testing](https://developer.mastercard.com/masterpass-merchant-integration-v7/documentation/masterpass-sandbox-testing-guidelines/index.md).

## Troubleshooting {#troubleshooting}

### Common Errors {#common-errors}

**204 Response**

* If you get a response of 204 when executing Masterpass **postback**then you have successfully called the result of a Masterpass transaction.

**400 Error**

* A response of 400 is a validation exception, meaning that a required field from the **postback** request is missing.

**403 Error**

* A 403 response (with HTTP Error Message "AUTHORIZATION_FAILED") may be returned because of an incorrect checkout ID in your request. If you see this error, check that you have used the correct checkout ID.