I suggest defining a separate payments table instead of making multiple copies of the same invoice. You can link one invoice or a group of invoices to as many related payment records as you need.
If payments are never made for more than one order, you can use this setup:
Orders::Order_ID = Payments::kf_Order_ID
If a payment can be made to pay off multiple orders, use this structure:
Orders::Order_ID = Order_Payment::kf_Order_ID
Payments::Payment_ID = Order_Payment::kf_Payment_ID
So there may be one "order" record, but many invoices. Each invoice record records the fact that you sent a receipt to the customer acknowledging their payment. Ok, I get that, hope you aren't duplicating all the data from Orders--you just need to link to it as you have already described.
How do you determine which Invoice records to pull up? That seems to be the main issue. Once you have performed a find or used go to related records to pull up that set of records and sorted them, moving from invoice to invoice is as simple as clicking a button set up to go to next record or go to first record.
I often add 4 navigation buttons for this when needed |< , < , > , >| as go to first, previous, next and last respectively. These all use go to record, but with different parameters.
Ah, that's right. I totally forgot about "go to record (next)" script.....
Right now I have it to set "go to related record" but when it changes the layout, filemaker goes and displays the correct invoice, but you can scroll through all other records. Would I have to perform a find and then go to related records?
Go To Related Records with the "Show Only Related Records" option specified should limit the found set do just those records that are related.