Just want to place it here so you know.
We found and fixed a bug -
Invoices for orders placed via X-Payments using Multicurrency show prices in primary currency regardless of customer selection
Patch is published at https://bt.x-cart.com/view.php?id=44506
4.7.1 will have this patch included out of the box, but older connectors will be updated as soon as we collect a bit more updates.
And yeah, you do not need to apply this patch if you do not see similar issue in your X-Cart 4.x integrated with X-Payments. If you do not know how to apply patches or afraid of doing it - contact our techs at email@example.com