Authorize.net - Invalid Notification

-- HikaShop version -- : 6.4.0
-- Joomla version -- : 5.4.3
-- PHP version -- : 8.2.30
-- Browser(s) name and version -- : Firefox 148.0.2
-- Error-message(debug-mod must be tuned on) -- : Invalid notification

On occasion we have a credit card transaction that is authorized via Authorize.net SIM, but shows up as declined in the backend. For the most recent case of this, the customer reported that they got an "Invalid notification" error when they made the payment. We were on Business 6.1.0 at the time and have just upgraded to 6.4.0. Maybe that issue has been corrected since 6.1.0, but I wanted to report the issue just in case it hasn't. We've seen this issue for some time with the Authorize.net SIM, but the vast majority of transactions don't have this issue.