You are trying to save an invoice but receive error "The Tax field cannot be left blank, even for non-taxable customers and sales which have no taxable items, so non-taxable sales will be correct for this district."
- Ensure the Tax Item (Sales Tax Settings) on the Customer Record is set to AVATAX
- If already set to AVATAX, change to something other than AVATAX then change it back to AVATAX then click Save
- Create a New invoice, don't click "Create a Copy". "Create a Copy" will retain the blank tax item field on the invoice