there is an account named something like “currency gain/loss”. So writing the difference off to that account would be different then writing it off to 'writing off" account (sorry not aware of the exact terms at the moment but they must be similar)
find a way to force the system to use your own defined exchange rate (>setup >currency exchange) rather then an automatically fetched rate
I am (due to a different problem) trying to figure this (#2) out for myself at the moment and can tell you more later maybe
It is returning the same SGD amount but you see, the USD amount will be different due to the exchange rate.
While using the write off is OK on the surface, you have to manually calculate the exchange difference, which defeats the purpose of having an ERP, especially if the transaction involves tax (another pain point).
Scenario is - I purchase 100 SGD, which is 97 USD.
One month down the road, I return it due to defect and got back my 100 SGD, which is at 96 USD now.
As such, in company currency, the company made a lost of 1 USD.
I have to:
Calculate the USD based on current month exchange rate
Calculate the difference between last month and current month (in company currency)
Book the difference via journal entry
Nonetheless, to do a Credit Note/ Debit Note based on the exchange rate of Purchase Invoice, instead of current document is conceptually inaccurate. The amount in company currency will definitely be different.