To remove a tax from an invoice, you just have to do the below steps.
Go to the Sales screen > Search for the SO number > Open the Order
In the SO screen click the Invoice Tab, and open the Invoice number.
In the right upper corner, you can see the Sales Order Settings, click the settings.
In the screen Update the Sales Tax % to be 0.00
Save the changes by clicking the Save button.
Close the Invoice screen.
Re-open the invoice number, and it should load and populate the changes. Tax should be 0.00
