Hello, George.
I appreciate adding as much details as you can regarding the gift card payment issue. I'd like to provide some information about the error code and how you can fix it.
Gift card payments are normally tracked under a liability account. Switching to another account might mess up your books.
Let's focus on the 6430 ValidationFault (Invalid Account) error code. This normally happens if a third-party app has restrictions on certain accounts when recording transactions (though QuickBooks will let you use liability accounts on sales forms).
You'll want to check your POS system and see if you can lift this restriction. Check your account mapping and settings and ensure the POS app is able to use the liability accounts on sales forms.
I would also recommend contacting your POS system's support channels. They have the resources to resolve the error message in their end, and help you transfer your data to QuickBooks.
After resolving the issue, do you need to reconcile your transactions and close out the current period? This article will help you with the steps and details: Reconcile an account in QuickBooks Online.
Need to record other transactions or need to take care of other imported data? Please let me know and I'll get back to you with some details and such.
