def METHOD_NAME():
    """
    Retrieves and return the Mattermost's configured api url
    :return:            String: the api url string
    """
    api_url = __salt__["config.get"]("mattermost.api_url") or __salt__["config.get"](
        "mattermost:api_url"
    )
    if not api_url:
        raise SaltInvocationError("No Mattermost API URL found")
    return api_url