@Frances3408 thank you for reading and replying. I did read the article via the link. It all is good information.
To us, the issue is that my wife logged on from within Australia - found the booking - all in AUD currency, forwarded me the link, I logged on with my account to book from US and the same dollar amount switched from AUD to USD. I didn't notice that the "AUD" was missing. I paid with her Australian credit card, and when we received the statement, the transaction amount was in $US, meaning the exchange rate now was factored in plus a conversion fee. Have you heard of this before?
Is it worth trying to discuss with Airbnb?
Thanks again for your kindness.