A Salesforce sandbox refresh will impact your Fullcast connection and settings. After the refresh, you'll need to manually reconfigure the application to ensure it works correctly.
Reconfigure the Salesforce connection
Check the tenant ID in custom metadata—in Salesforce setup, navigate to Custom Metadata Settings > Fullcast Setting and check the Tenant ID.
Recreate the external client app and reconnect Fullcast—a sandbox refresh can invalidate the external client app and its Fullcast connection. Follow Create the external client app in Salesforce onward in Migrate from connected app to external client app to recreate the app (if it didn't carry over from the refresh) and reconnect Fullcast to it.
Import a job—run a full import job to confirm the connection is successful and update the data in Fullcast.
Once this is complete, you can resume sandbox work, such as testing routing policies.