Nothing has changed since 2017.

But here's a way to do what you want, thinking way outside of the box.

Let's say the prepaid expense accounts are in the 1900 to 1999 range, department blank. You create 12 accounts for each related expense - 19XX-1, 19XX-2 ... 19XX-12, where the XX would link to the appropriate expense account (for example account 19TR), and the suffix is the department. Balance Sheet accounts don't generally have departments, so this should not conflict with anything.

In your example, when you enter the flight payment in January, you would code it to 19TR-12 because it's going to end up in December. And there it sits, displaying on the balance sheet with the other 19XX accounts, consolidated into one line.

Here's the trick. Set these prepaid accounts up as reallocation accounts, all twelve of them identically set up to reallocate to the appropriate expense account 100% (for 19TR each would reallocate to travel expense).

As part of month-end steps, in Ledger, you run Maintenance | Create Reallocation Batch, just for that month's department. So in December, it will be 19AA-12 to 19ZZ-12. It will automatically move the balances from prepaid for all of the department 12s to the appropriate expense, zeroing out the prepaid balance. It won't touch the other months' department balances.

One downside - it will only work for prepayments that are spread over 12 or fewer months. But they don't have to be within the same fiscal year.

Steve