Hello, meg-archer. 

Paying the invoice using an International bank is currently unavailable in QuickBooks Online. As for now, our Merchant services accept only the US bank. Nothing to worry, I'll personally tap to our developers so they might consider adding this feature on any future updates.  

In the meantime, you can visit our Blog site. This is where we share recent happenings and future developments, such as updates to newly added features. Here's the link: The QuickBooks Blog.     

As a workaround, let your customers use other apps like PayPal or other apps that are supported in QBO. Go to this link: https://apps.intuit.com/app/apps/search?searchTerm=ach. In this link, you can see the approved apps that you can use in paying invoices through ACH.   

For future reference on how to process an ACH bank transfer for your customer’s sales receipt or invoice in QuickBooks Online, please check this article: Process an ACH bank transfer from a customer. 

Please let me know if you have other concerns with ACH payments or questions about QuickBooks. I'll be around to help you out. Take good care and stay healthy!