We use both ConnectWise and QuickBooks online. When saving transactions in ConnectWise, they are pushed to QuickBooks online in a batch.
After the transactions arrive in QuickBooks online, they have no tax on them and no AvaTax tax line.
In order for transactions that are pushed into QuickBooks Online from an external source to have AvaTax calculate tax, you would need to manually hit the Estimate Tax button in Quickbooks Online
This is due to limitations within Intuit's API regarding automatic calculation with 3rd party tax engines, such as AvaTax, for transactions pushed into QuickBooks Online from an external source.