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API authentication uses Basic Auth with an API key. Enter your API key in the username field and leave the password field blank. Requests should include an Authorization header in the form Basic base64(<API_KEY>:), where the colon is required even though no password is provided. Most HTTP clients (such as Postman, see screenshot below) will generate this automatically when you select Basic Auth, input the API key as the username, and leave the password empty.
Basic Auth selected in Postman, with the API key as the username and the password left empty
With curl, pass the API key followed by a colon to -u:
A request with a missing or invalid API key returns a 401.

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Environments

API keys are issued per environment. A sandbox key only works with the sandbox base URL, and a live key only with the live one. The examples in the API reference use the live base URL, so swap in the sandbox one while you test. See the Sandbox Guide for how the sandbox differs from live.

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Getting an API key

To obtain your API key if you do not have one already, please reach out to developer-support@theguarantors.com. See Request an API key for what to include.