How to handle Audit Fee provision by month for whole year?

Hi All Experts

Please help what is the best way if our client wants to post in Purchase Order 1 year ahead before actual AP invoice 1 year later for Debiting Audit fee Credit Accruals Provision for Audit Fee for prorating estimation monthly Audit Fee till final AP invoice will Debit total Provision of Audit Fee Credit Accounts Payable, possibly some difference when need to Debit additional expense Credit Accounts Payable in the final AP Invoice receiving 1 year or 1 and half year later.

Currently they are using manual Journal Entries to post such Audit Fee provision and manual reversal to AP Invoice.