Issue
Your Heroku Connect add-on is in the INACTIVE_ORG state and is not syncing data. You've received an email notification informing you that your Salesforce organization has become inactive, either due to a subscription with Salesforce ending, licenses expiring or a sandbox refresh.
Resolution
Check if a sandbox refresh happened
When a sandbox refresh happens, the Salesforce organization ID changes. In this case, you will need to follow these instructions to create a new connection. It's not possible to re-use your old connection. You can determine if your Salesforce organization is in a production or sandbox environment under the ENVIRONMENT label in the Overview tab of the Heroku Connect dashboard. If the Salesforce organization is in a sandbox environment, you can determine if a sandbox refresh happened by following the instructions in this article.
Check if the org was deactivated
If the Salesforce org is a production environment, or is a sandbox and a refresh didn't take place recently, it is more likely that the org was deactivated for a period of time. That can happen for several reasons, including a subscription with Salesforce ending, or licenses expiring. To determine if that is what happened, log into your Salesforce org, go to Setup and search for Company Information. There you can find the status and status history for your org. If you confirm that your Salesforce org was locked for a period of time but is now active again, contact Heroku Support to reactivate your connection in Heroku Connect. If you can't log into your Salesforce org, contact your Account Executive.