Hi there jason-kwon-avesd,
Thanks for reaching out about payment made by your customers. QuickBooks Online is a great tool able to help you create and send invoices to your customers so they know the amount owed for your services. I can provide some information about multicurrency invoices.
With QuickBooks Payments, it's only possible to process payments in CAD currency. That would be why when creating an invoice or transaction in USD or any other currency, you won't see the box to check to process payments. These payments with other currencies would need to be processed outside of QuickBooks Payments.
If you have any other questions, feel free to reach out here.