You are posting a Purchase Invoice and see the following in the Activity Logs in Concur Invoice
"Overcharged. Tax calculated by AvaTax is equal to Concur. Avalara calculated tax: 0, Vendor bill tax: 0.00"
There is no issue with the Avalara AvaTax connector for Concur Invoice. This functionality is as per connector design.
For returns filing, you can generate the "Tax Variance" report from "Standard Consumer Use Tax Reports" section. It will be done automatically if you use Avalara Returns for filling. Otherwise you can download these reports from the Admin Console to see the "Tax Variance".