Which function are you using for Supplier Invoice? Purchasing or AP/AR Accounting? If you are using Purchasing, it is not supposed to be entered, it should be converted from Purchase Orders or Receipts. If you are using AP/AR, then probably with some development you can achieve what you need! Need help on that?

AP/AR entry. Yes, I will definitely need help.

Can't you duplicate the record, by simply deleting the number and pressing tab, this way starts the creation of a new record...

1.Select a record of a Supplier Invoice for your desired Supplier;
2.Delete the number of the record/Invoice;
3.Press tab;
4.Change or update the data necessary;

We’re not trying to duplicate an invoice, we want to enter batches of invoices which include multiple invoices to the same vendor.