When trying the sample from https://github.com/microsoft/opentelemetry-azure-monitor-python/blob/master/azure_monitor/examples/metrics/observer.py I get the error

TypeError: Object of type 'Envelope' is not JSON serializable..

My current hack/workaround is to update this function
def _metric_to_envelope( self, metric_record: MetricRecord ) -> protocol.Envelope:

in this file https://github.com/microsoft/opentelemetry-azure-monitor-python/blob/master/azure_monitor/src/azure_monitor/export/metrics/__init__.py

to return a dictionary.
return envelope.to_dict().