Help with VBA to input data into a second sheet using formulas

I really have no idea where to start trying to stitch something together for this.

I have a Honey and Honeybee business, I am getting ready to start offering gift certificates and gift cards (gift cards are online and handled by Square). I have a sheet for the gift certificate serial numbers (barcodes) apart from the UPC-SKU sheet.
On the Gift Certificate Register ("GC Register") sheet, I have formulas to calculate how much of the gift certificate was used and to tally a balance based on if Column A of the GC Register sheet is >0 OR (with a countif) GC Register A:A = Invoice A13:A43. Being they are IF statements, unfortunately they are dynamic so when I run my macro to print, save and create a new invoice, the values from the formulas are no longer present. And here lies my query.

I need help with creating a macro to search or match is a gift certificate serial number has been entered on the invoice, find the cooresponding serial number and input the values of how much of the gift certificate was used and a balance.

The formulas I am using are:

Amount Used:
=IF(OR(A2>0,(COUNTIF(Invoice!$A$13:$A$43,A2))),IF(G2>SUM(Invoice!$F$13:$F$43),SUM(Invoice!$F$13:$F$43),IF(SUM(Invoice!$F$13:$F$43)>G2,G2)))

Balance:
=IF(COUNTIF(Invoice!$A$13:$A$43,A:A),IF(SUM(Invoice!$F$13:$F$43)>=G2,0,SUM(G2-SUM(Invoice!$F$13:$F$43))))

I used the OR function in the above formula only to always display a value and not "FALSE" in the cell.

I've attached the very stripped down version of the workbook, any help will be greatly appreciated!

Thanks,
Greg

If a Gift Certificate can be used against more than one invoice, then I suggest that you record the Invoice numbers in the "GC Register". In Invoice descrition I would record as "Gift Certificate " followed by name/customer number: "Gift Certificate - John Smith"

I notice you keep a monthly (or it appears to be) invoice register: again I would keep an annual register. Equally, if the invoice amount is covered by a GC, then considedr recording this in the (Invoice) register.