Thanks @thhtev and @C_Billings. I did install AvaTax for SuiteTax bundle (in SB) after we turned on SuiteTax but I'm getting an AvaTax error "This Document has used AvaTax Services. Company not found." I made sure the connection is working in our SB account. I asked NS Support and Avalara Support but none of the suggested solutions worked..

This happens daily in our Sandbox account. I must reconnected it by going through the Manage Avalara Setup. Edit credentials and go through the process. production account is fine though.

@evelet, Have you mapped company under AvaTax? If company is not mapped you will receive this error message for sure.

Looks like the mapping is missing as already suggested - the mapping also fails if auth fails so both suggestions are sound. It seems a little erratic when this happens but at one point I made a habit of re-authing/checking mapping before any testing on tax at all just to be sure.

thank you both. We were missing the Avalara for SuiteTax connector.