Hi LisaJW
Thanks for joining us here on the Community. :)
We currently have a reported investigation for this issue 'INV-52988 - Pay Bills via + New will not provide the box for Exchange Rate and when Bill Payment is saved, exchange rate shows up as "1"' and our technicians are currently working to fix. We have linked you to this so that you'll be notified as soon as this is resolved via email.
As a workaround in the meantime, you can go to expenses and open the foreign bill(s) and click 'Make Payment' for the system to show the exchange rate and the 'Exchange Gains or Loss' will be calculated as expected.
Please get back to us below if you have any Q's!