Good morning, @fromthedeskoflex,
That's a great question! Merchant services can accept payments from your international customers. However, the customer will have to enter a 5-digit card that would be provided by their card-issuing bank. If they don't have that code, they would need to contact their card-issuing bank to have that number issued to them.
Here's an article with some more information about accepting payments from international customers:
Accept Non-US credit card from customers using QuickBooks Merchant Services
Hope that helps!
Lucas