I have about 500,000 in A/P that will not be paid due to multiple issues but we have paid all the gst on it already. How do input it now to get that gst back?
Being proactive in ensuring everything is set up correctly for your sales tax filings is a great habit. The tax centre is one of QuickBooks Online's most powerful features, so I'm happy to see you're using its full potential. Under accrual basis accounting, taxes are filed in the period they were charged regardless of when (or if) they were paid. Using advanced tracking for exceptions, any transactions deleted or changed will be represented on your next filing. You can read more about exceptions in this handy article: Sales tax exceptions
Sorting out sales tax is work best suited for an accountant. They're a valuable partner who'll know how to write this off in a way consistent with your local tax laws. You can easily invite your accountant as a user to approach this together. To search for a pro in your area, simply head to the My Accountant tab in QuickBooks Online then click on Find a pro to help.
Feel free to reach out if you have any additional questions.