Does the accounting system also accept US dollars?

I always convert my purchases in USD to EUR using the exchange rate on the invoice date.

Yes, but what about Bitcoins, for example, which have a fluctuating exchange rate? ☺

The same. USD also has a fluctuating exchange rate compared to EUR, for example.You should indeed use the exchange rate of the virtual coins on the invoice date (but be careful, because if payment is made later, this can make a big difference, both positive and negative), unless you have the payment made automatic on the invoice date (or issue the invoice on the payment date).

Johan