khay4 said:

None of these invoices have payments on them yet, strictly A/R and A/P.

That may be but it sounds like you are ignoring my advice.  The only way to show an historical entry is no longer owing that amount of money is to post an Historical Payment from the Customer Ledger as you did the original Historical Invoice.  An invoice of $100 and a payment of $100 means nothing is owing and you can then reenter it with a slightly different invoice number.  If the original invoice is #12345 then enter the new one as #012345.  There is no way to edit the entry with the Sage 50 user interface.

If you are not sure about doing something, take a backup of your file and try it on the backup copy (File, Save As and give the file a different name as you would an Excel spreadsheet if you wished to make a copy) or create new test file.

Okay I misinterpreted you there at first.

So how do you go about doing this?

At the moment I am just entering my Customers and Vendors, recording all the transactions that are outstanding and leaving it at that and it seems to be working correctly other than the fact I cannot adjust. They are still owing (or we are still owing in payable cases) of the money. 

Could you please elaborate on what needs to (or should be) done differently.

Thanks

For others reading this, I was already done the images so I thought I would post them anyway.

Posting historical invoice payments.  Just enter the payment amount against the invoice and make sure the date is before the start date of using Sage 50.

Posting Historical Invoices in USD.  Note the boxes for USD, Exchange Rate and CAD.  Fill in USD and exchange rate and CAD calculates.