Use a stable item ID and record the vendor, invoice number and date, description, prepaid account, expense account, original amount, service start and end dates, and document link. Add the approved recognition method and monthly amount. If one invoice covers several services or departments, split it into schedule lines when their service periods or coding differ.
The accounting policy belongs outside the spreadsheet. An authorized controller or accountant should determine which costs qualify as prepaids, any threshold, and whether recognition is straight-line or follows another pattern. The bookkeeper applies that approved policy and flags facts that do not fit it.