Yes, I instructed the client to clear their cache, or use a different browser.  They able were not able to figure it out and ended up paying by check.  They shouldn't have to fiddle with their browser.  Been paying invoices online for decades, have never had to clear the cache for a payment to go through.  What sort of data is QuickBooks trying to collect from the cache? 

Seems like this is fixable on Quickbook's side.  My customers shouldn't have to jump through hoops to pay their bill.