You recently opened up your Quickbooks with the Avatax for Quickbooks integration, and received a notification that the certificate is expired.
The approval of the certificate required by QuickBooks to allow a 3rd party integration to gain access to the QuickBooks Company File is normally part of the installation process. In cases where clearance has been removed for 3rd party applications (Including AvaTax, or AvaTax ST), the certificate may require re-authentication.
If prompted to re-authorize the certificate, which QuickBooks will do by producing a pop-up message titled "QuickBooks - Application with Expired Certificate", the user will need to select "Yes, whenever this QuickBooks Company File is open". This selection will allow the authorization of the certificate automatically each time that Company File is open. Once selected, simply click Continue, and then click Done on the confirmation pop-up.
Upon the completion of this process, the AvaTax connector will work as intended.