After “how much does this customer owe?” a shop that takes two currencies asks a second question: how much is out there altogether? You cannot add riyals to pounds. You pick a base — usually dollars — so you can see one total.
That dollar figure is not a live ticker, and it is not what you print on their statement if you deal with them in pounds. Each entry stays in the currency you actually took. The dollar total sits to the side so you can decide.
A weekly rate from your market is enough. A line with no currency ruins any total. If everything is already in dollars, don’t add a conversion you don’t need. See how much they owe.
In Kaymn entries stay in their currency; the USD equivalent is for you — start the trial.