Posting a Journal That DO NOT balance in FX but DO balance in LCY

One of my customer want to be able to post a general journal that do not balance in foreign exchange but do balance in LCY,

example :

Account GL No. Currency Code Debit Credit Amount LCY
X USD 500 750
Y USD -450 750

I’ve tried a few things but Navision always seems to chech that my FX amount balance