AWS Lambda to start and stop ec2, endpoint connectionerror

I have followed the article in setting up AWS Lambda to stop and start my ec2 instance but I get following error while doing test run

Test Event Name stop

Response { "errorMessage": "Could not connect to the endpoint URL: "https://ec2.ap-northeast-2a.amazonaws.com/"", "errorType": "EndpointConnectionError", "stackTrace": [ " File "/var/task/lambda_function.py", line 7, in lambda_handler\n ec2.stop_instances(InstanceIds=instances)\n", " File "/var/runtime/botocore/client.py", line 530, in _api_call\n return self._make_api_call(operation_name, kwargs)\n", " File "/var/runtime/botocore/client.py", line 944, in _make_api_call\n operation_model, request_dict, request_context\n", " File "/var/runtime/botocore/client.py", line 966, in _make_request\n return self._endpoint.make_request(operation_model, request_dict)\n", " File "/var/runtime/botocore/endpoint.py", line 119, in make_request\n return self._send_request(request_dict, operation_model)\n", " File "/var/runtime/botocore/endpoint.py", line 207, in _send_request\n exception,\n", " File "/var/runtime/botocore/endpoint.py", line 361, in _needs_retry\n request_dict=request_dict,\n", " File "/var/runtime/botocore/hooks.py", line 412, in emit\n return self._emitter.emit(aliased_event_name, **kwargs)\n", " File "/var/runtime/botocore/hooks.py", line 256, in emit\n return self._emit(event_name, kwargs)\n", " File "/var/runtime/botocore/hooks.py", line 239, in _emit\n response = handler(**kwargs)\n",