There was a problem exporting the parent customer for this invoice

Are you seeing an error that suggests there is an issue with the customer record when syncing? This can sometimes be easily resolved by changing your setting to "Edit contacts in Quickbooks" and running a sync with nothing in the ready to sync queue.
To change this setting go to: Settings> Integrations> Quickbooks.
The error may still appear on the invoice until it syncs over. We're standing by to assist further if that does not do the trick.