We have recently seen a rash of Certificate Expired messages from people using QB POS v 18, and QuickBooks Desktop 2020 ( and older versions).
This is happening because the connectors in the background are using certificates that have an expiration date. That date has been reached.
On current versions of the software, the certificate would be replaced with a version that has a future expiration date.
Because the QB POS v 18, and the older versions of the QuickBooks desktops are discontinued, there are no updates to reset the certificates expirations dates.
Intuit has released a statement that Microsoft has agreed to temporarily extend the certificates. You can download and execute a zip file at :
intuit.me/cert or https://quickbooks.intuit.com/learn-support/en-us/help-article/web-integration/fix-error-quickbooks-application-revoked/L6Y849bKg_US_en_US?uid=llv2o5o9
If this does not work, you may need to enter data from the QBPOS into your QuickBooks desktop software, you will need to do so manually.