If you're shown that the export contains errors, you'll find all errors under Settings → Shop → Pickware Import/Export Module in the detail view of the respective export.
To make sure the orders are included in the next export, it's usually enough to check the individual line items and add additional accounts in the configuration for the respective business transaction.
With our DATEV module, it will also be possible in the future to create multiple exports for the same business transactions within a period, so that the documents will be included in the next export after adjusting the configuration.