How to provide dimensions to a metric?

[jackiecheng2008]

I use AWS PowerTools (aws-lambda-powertools==1.18.0) in Python Lambda; Python version is 3.8.
I need to specify an Error Code and an Error Message to each metric; below is my code:
with single_metric(name="metricName", unit=MetricUnit.Count, value=1, namespace=myNamespace) as metric:
metric.add_dimension(name="error-code", value='C-E-6299')
metric.add_dimension(name="error-message", value="DLQ Error: Message failed to send back to SQS")
ptMetrics.add_metric(metric)
But I always received below error:
[ERROR] TypeError: add_metric() missing 2 required positional arguments: 'unit' and 'value'
Traceback (most recent call last)

What's wrong? Or what's the correct way to achieve this?

[jackiecheng2008]

If I use standard metric as below:
metrics.add_metric(name = 'RawS3MessageFailed', unit = MetricUnit.Count, value = 1)
There is no way to add dimensions, correct?
I read the reference here about single_metric but no where mentions how to use this single_metric after adding dimensions in it.
Please help!

[jackiecheng2008]

It seems like no need to add; below line is useless:
ptMetrics.add_metric(metric)