Time out on CloudWatch PutLogEvents

[edwinc-passiv]

Hello,
I'm having trouble putting logs into CloudWatch against a specified log group and log stream. My Lambda includes the following code and it always times out with the error message "curlCode: 28, Timeout was reached"

In my main.cpp I have

 Aws::SDKOptions options;
  options.loggingOptions.logLevel = Aws::Utils::Logging::LogLevel::Trace;
  Aws::InitAPI(options);
  {
// call function
  }
  Aws::ShutdownAPI(options);

and in the called function I have

Aws::CloudWatchLogs::CloudWatchLogsClient cwl; 
Aws::CloudWatchLogs::Model::PutLogEventsRequest request;
request.SetLogGroupName("testloggroup");
request.SetLogStreamName("testlogstream");
Aws::CloudWatchLogs::Model::InputLogEvent log;
log.WithTimestamp(Aws::Utils::DateTime::Now().Millis()).WithMessage("Hello cloudwatch");
request.AddLogEvents(log);
request.WithSequenceToken("fake");
auto outcome = cwl.PutLogEvents(request);

and the outcome.GetError().GetMessage() is the time out error above

I've also tried the code suggested in issue #1470 with

    config.region = Aws::Region::US_EAST_2;
    auto m_client = Aws::MakeUnique<Aws::CloudWatchLogs::CloudWatchLogsClient>("cloudwatch Client", config);

but it makes no difference.

My log group "testloggroup" and "testlogstream" are set up manually in CloudWatch.

What am I missing?
Apologies, I'm a bit of a newbie and it maybe I have some other AWS thing set up wrongly, but I'm stuck because I don't get anything other than the time out.
Many thanks in advance.