My Lambda function creates EC2 servers via the create_instances module of boto3.

I have been triggering this Lambda since morning, and it was creating instances well and good. But suddenly, I keep getting this weird error:

{ "stackTrace": [ [ "/var/task/processing.py", 54, "lambda_handler", "KeyName=keyname, SubnetId='subnet-<>', SecurityGroupIds=['sg-<>'])" ], [ "/var/runtime/boto3/resources/factory.py", 520, "do_action", "response = action(self, *args, **kwargs)" ], [ "/var/runtime/boto3/resources/action.py", 83, "__call__", "response = getattr(parent.meta.client, operation_name)(**params)" ], [ "/var/task/botocore/client.py", 251, "_api_call", "return self._make_api_call(operation_name, kwargs)" ], [ "/var/task/botocore/client.py", 537, "_make_api_call", "raise ClientError(parsed_response, operation_name)" ] ], "errorType": "ClientError", "errorMessage": "An error occurred (RequestExpired) when calling the RunInstances operation: Request has expired." }

What has happened? Pretty sure it was not the code mistake, as the same code well was running since morning.