public async Task TooManyRequests()
{
    var client = new RestClient("https://httpstat.us/429");
    var request = new RestRequest();

    var context = new Context().WithLogger(_logger);
    var response = await Policies.AsyncRateLimit().ExecuteAsync(ctx => client.ExecuteAsync(request), context);
}

public static AsyncRetryPolicy<RestResponse> AsyncRateLimit()
{
    return Policy.HandleResult<RestResponse>(response => response.StatusCode == HttpStatusCode.TooManyRequests)
        .WaitAndRetryAsync(RateLimitRetryCount,
            (attemptCount, restResponse, _) =>
            {
                var retryAfterHeader = restResponse?.Result?.Headers?.SingleOrDefault(h => h.Name == "Retry-After");
                double secondsInterval = 0;

                if (retryAfterHeader != null)
                {
                    var value = retryAfterHeader.Value?.ToString();
                    if (!double.TryParse(value, out secondsInterval))
                    {
                        secondsInterval = Math.Pow(2, attemptCount);
                    }
                }

                return TimeSpan.FromSeconds(secondsInterval);
            },
            (response, timeSpan, retryCount, context) =>
            {
                var logger = context.GetLogger();

                logger?.LogTrace(
                    "The API request has been rate limited. HttpStatusCode={StatusCode}. Waiting {Seconds} seconds before retry. Number attempt {RetryCount}. Uri={Url}; RequestResponse={Content}",
                    response.Result.StatusCode, timeSpan.TotalSeconds, retryCount, response.Result.ResponseUri, response.Result.Content);

                return Task.CompletedTask;
            });
}