Katana updates currency rates daily for your open orders, but the rate is fixed in certain situations.
From a business perspective, the currency rate should typically be fixed at the moment of creating a bill. Katana does not have an accounting module, but Katana will fix the currency rates on orders at the moment when you are likely to create the bill in your accounting system.
Katana will automatically fix your currency rate if:
The Purchase order (PO) is set to Received or Partially received.
The PO is pushed as a bill to accounting software (Xero, QuickBooks).
Sometimes you may need to manually edit the conversion rate and you learn how to do that here.
Fixing the currency rate on a "Partially received" order
When an order is Partially received, the currency rate is fixed for the part that has been received. Items that haven't been received still use the daily exchange rate. Receiving Purchase orders partially can result in every received part having a separate currency rate as they were received at different times.
Example of a PO with partially received items:
Billing partially received orders in foreign currency
When issuing a bill for Xero or Quickbooks Online for an order that has been partially received then Katana will adjust the conversion rate on all received parts of the order.