Not sure why you are getting no data.
RequestReport
<?xml version="1.0"?>
<RequestReportResponse xmlns="http://mws.amazonaws.com/doc/2009-01-01/">
<RequestReportResult>
<ReportRequestInfo>
<ReportType>_GET_FLAT_FILE_ORDERS_DATA_</ReportType>
<ReportProcessingStatus>_SUBMITTED_</ReportProcessingStatus>
<EndDate>2018-06-17T07:00:00+00:00</EndDate>
<Scheduled>false</Scheduled>
<ReportRequestId>xxxxxxxxxx</ReportRequestId>
<SubmittedDate>2018-07-03T20:56:06+00:00</SubmittedDate>
<StartDate>2018-06-10T07:00:00+00:00</StartDate>
</ReportRequestInfo>
</RequestReportResult>
<ResponseMetadata>
<RequestId>xxxxxxxxxxxx</RequestId>
</ResponseMetadata>
</RequestReportResponse>
GetReportList
<?xml version="1.0"?>
<GetReportListResponse xmlns="http://mws.amazonaws.com/doc/2009-01-01/">
<GetReportListResult>
<HasNext>false</HasNext>
<ReportInfo>
<ReportType>_GET_FLAT_FILE_ORDERS_DATA_</ReportType>
<Acknowledged>false</Acknowledged>
<ReportId>xxxxxxxxxx</ReportId>
<ReportRequestId>xxxxxxxxxxxx</ReportRequestId>
<AvailableDate>2018-07-03T21:00:16+00:00</AvailableDate>
</ReportInfo>
</GetReportListResult>
<ResponseMetadata>
<RequestId>xxxxxxxxxxxx</RequestId>
</ResponseMetadata>
</GetReportListResponse>