We are currently working on a new stored procedure called "sp_lastinsertdata" which will return all the lines of an invoice from QuickBooks if you do:

sp_lastinsertdata InvoiceLine

after your last inset for each invoice. This will allow you to check the contents of the invoice, but more importantly, you will be returned all the values QuickBooks adds like TimeCreated, TimeModified, Sequence etc. that will allow you to mirror the complete transaction in your external system (if required).

If you are creating invoices by just using InvoiceLine inserts without using group items, run:

SP_LASTINSERTID invoiceline

and grab the TxnID and do:

select Top 1 TxnID, InvoiceLineTxnLineId, InvoiceLineSeqNo from InvoiceLine
where TxnID='5D43-1197768681' order by InvoiceLineSeqNo Desc

Otherwise, if you do invoice group items you will need to do something like this:

select Top 1 TxnID, InvoiceLineTxnLineId, InvoiceLineSeqNo from invoiceline
where TxnID='5D43-1197768681' and InvoiceLineTxnLineId is not null
order by InvoiceLineSeqNo Desc

but if you are the only one creating invoices at the time, simply jump the gun by just doing:

select Top 1 TxnID, InvoiceLineTxnLineId, InvoiceLineSeqNo from invoiceline
where InvoiceLineTxnLineId is not null
order by TimeModified DESC, InvoiceLineSeqNo Desc

BTW: You can leave out the null test if you don't use Itemgroups.