Hi. I'd like to know if it's possible to carry a balance to a new invoice for the same customer. Currently when I make up a new invoice it doesn't show the balance due from the previous invoice. Any help with this would be greatly appreciated.

You will need a self-join relationship of Invoices for this, defined as:

Invoices::CustomerID = Invoices 2::CustomerID

AND

Invoices::InvoiceID > Invoices 2::InvoiceID

Sort the records on the Invoices 2 side of the relationship by InvoiceID, descending. This will make sure the last invoice for this customer is the first related record from Invoices 2.

Now you can define a PreviousBalance field in Invoices as a lookup from Invoices 2::Balance.