Is there a way to ensure vendor ACH data saves correctly in for a vendor within Quickbooks Online?

Try opening your QBO account on any private/incognito browser.

Warm greetings, seamusiclover.
 
It looks like you previously posted a similar query, and my colleague has already provided an answer with detailed information on entering vendor ACH details. You can view their response by following this link: https://quickbooks.intuit.com/learn-support/en-us/reports-and-accounting/how-can-i-manually-enter-ve...
 

Additionally, you can run vendor reports to get an overview of your accounts payable transactions.

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This 'Additionally, you can run vendor reports to get an overview of your accounts payable transactions.' has nothing to do with my question.

Another option, sign up for a Melio account to compare and it's more reliable. You can ask your vendors to register their ACH details online to avoid errors. You can also get the cashback to pay bills.

https://quickbooks.intuit.com/learn-support/en-us/reports-and-accounting/has-anyone-been-able-to-set...

Hello, @seamusiclover.

I appreciate you taking the time to explore the additional sources provided by my colleague. Let me add more about the uses for this reference.

Here in the QuickBooks Community, we aim to provide comprehensive responses, while also offering recommendations and anticipating your future needs. This is where these Community articles comes in. It is intended to help you gain an overview of your business performance for future references.

To add more on this topic, check out this article to learn how much you're paying each vendor on a monthly basis: How to run and save a monthly expense report by vendor.

If you have any further questions regarding QuickBooks Online or any related concerns, please feel free to reach out. We are here to assist you at any time.