2 choices: enter as a purchase invoice, code the invoice to prepayments 1103 in the balance sheet and then each month journal 1/12 to rates 7102. Each payment from the bank reduces the trade creditor in the balance sheet
Or
Enter as 12 individual invoices, each dated for the 12 months of the year in suppliers all with the same reference in the next box to the date (just F6 to copy the box above). This will automatically add the transactions together in the suppliers account to equal the invoice but post each invoice in the relevant month. Pay it off through the supplier account from the bank as above to reduce the creditor