Hello, skylargraceco. I have some steps that will help ensure that your clients can make payments via bank transfer. 

Let us first isolate this issue by performing troubleshooting steps to check if this has something to do with browser-related problems. Some of the temporary Internet files on your computer can become corrupted and outdated, resulting in browsing issues and other errors like the one that your customer experienced.

To begin, allow your client to access the payment link via a private window to process the payment. Here are the keyboard shortcuts they can use depending on the browser they are using:

• Google Chrome and Microsoft Edge: press Ctrl + Shift + N 
• Mozilla Firefox: press Ctrl + Shift + P
• Safari: press Command + Shift + N 

If the payment went through without error, they can return to the regular browsing window and have the browser's cache cleared. They can also use other supported browsers as an alternative.

I've also checked and confirmed that there have been no reported issues with the error message when clients pay invoices through bank transfer. 

If you have any other problems with ACH payments, you can use this article as a reference to resolve them: Fix rejected ACH payments or fees in QuickBooks Payments.

Let me know if you have other concerns or questions about payments. I'll be here to assist.