It should be possible. Likely you will use a calculation field that will get the total paid from another table or even sum up the payments from a payment table.
Sorry I have been using filemaker for about 3 years now and just learn as I go, never really had training so I have never modified an existing template. We have an invoice template that needs to be modified to show the balance paid calculated into the total balance owed after a percentage of it was paid. I need filamaker for dummies basically. lol step by step instructions on how to add balance paid in the totals column. does this make sense or do you need more information?
If i have to pay to call customer support i might just have to but if i can get help on here that would be great!