Customers has below scenario when they use budget on purchase order invoice:

Their fiscal year on the ledger is from January to December. But budget year is from April to March of next year. At purchase order side, they have purchase invoice need post, for example, post at Nov-2023 (Posting date on PO invoice is in Nov-2023). But because this purchase order need consume budget of whole budget year, then they set the Accounting date on the purchase order as 31-Mar-2024 (It’s last day of this budget year, but it’s next year of fiscal year.). Then, when they post the purchase order invoice at Nov-2023, system will throw error "The accounting date for the invoice must be in the same fiscal year as the related purchased order. Run the purchase order year-end process or change the date to the current fiscal year.". 

Customer expect application should support such scenario, when posting, application shouldn't prevent with error, and it should consume the budget based on accounting date well.