One approach would be to export a list of invoices from FMS and then to filter on the supplier name:
Reports > Accounts Payable > Invoices > Invoice and Credit Note
Select Detailed and the Financial Year and sequence by Supplier Name
Export as a full report, csv and save in a year-end folder.
Open the report, highlight row 1 and add a filter.
Filter column A to select counter party suppliers.
Filter column A and remove any VAT codes (the required totals should be net of VAT
The net totals should then be found in column R.
This will give a total for invoiced expenditure. Consideration should also be given to prepayments, accruals and cashbook entries.