Katana allows you to edit the currency conversion rate after it has been fixed so you can modify and recalculate the converted total if needed.
This is usually required when you need to match exchange rates between two systems or to match with the currency conversion rate of the actual payment that was made.
Read here about when Katana fixes your currency rate.
How to edit currency rate on my Sales Order
1. Open a Sales Order that has foreign currency as order currency. When the currency rate is fixed, you see the "Edit rate" link.
2. Click on "Edit rate" under the Totals section of your Sales Order and edit the "Currency rate" or "Fixed at" date.
PS: Changing the fixed date will not retrieve the currency rate for that date (in the past) and will not update the currency rate to your selected date.
3. After changing the conversion rate the Converted Total (Base Currency) will be recalculated.
Why cannot I change my conversion rate?
When the order was already submitted to accounting as an invoice or as a bill (via accounting integrations) then it is not possible to change the rate in Katana anymore. This should now be done already in your accounting platform.