Here's a guide to how foreign currencies are handled in Unity:
How does Unity convert an invoice submitted in a foreign currency into the currency used in my Unity environment?
Unity supports nearly every currency in the world identified by the ISO standard currency system. Our system uses https://openexchangerates.org currency conversion data API to convert currency nightly.
At what point does Unity lock down the rate so that the amounts do not change (at the time of invoice submission, approval, etc.)?
Once the vendor submits an invoice, Unity stamps the invoice with that rate. The rate does not change after stamping.
Is there somewhere in Unity that the customer can see the exchange rate that was used to convert an invoice?
The customer can see the submitted amount and the converted amount. Then, they can do the math to obtain a relatively accurate value.
Is there a way to change the currency conversion rate in Unity to a month-end average rate?
No. We only use daily rates, as described above.
What restrictions does Unity have on invoices and currency?
Only invoices submitted in US dollars can be adjusted manually or through automated rules.