prepayment with exchange rate

Jpn

i found a problem when using prepayment with exchange rate. let say i create prepayment invoice with 20 usd(800 lcy) then when goods come, i post receive and invoice for that goods ...system will create negative line of prepayment with -20 usd(-900 lcy)<-- following exchange rate for goods so prepayment account wil be -100 but in reality, it should be 0.
any solution for this case?? now i let my customer to adjust it in general journal.

kapil4dynamics

If prepayment is less than 100% and ur rates have changed at the time of receipt and invoice from the rates mentioned at the time of prepayment then system will show u some balance.