Change due issue with foreign currency

[AstonMark]

Hi Guys,
Have an issue while settling in foreign currency.
Dealing with 2 currencies. ZMW and $.
The default one is ZMW.
But as in the picture, the transaction is not getting settled in $.
Instead of showing the change due. It is showing the total amount in ZMW.
Can someone help me out with this??

[AstonMark]

I changed the decimal places as follows and now it is working.
May i know whether this is the proper method?