Reverse/recalc sales tax paid to the state on an invoice that was cancelled/voided

@Dave500 

Anytime you need to "void" an invoice from a previous period (month/year), the proper way to do that is to create a credit memo in the current period (April) that offsets the original invoice (March) and then apply it to the invoice.  That will reverse and close the invoice in April and give you a credit for the amount of sales tax.

At this point, there's nothing you need to do.  When you voided the invoice, it removed the $200 sales tax payable liability, but not the payment made to the state, thereby giving you credit for the payment.  To confirm that, run a balance sheet report and click on the amount next to your sales tax payable liability account.  That will pull up all transactions that posted to sales tax payable.  You should see that the original invoice that you voided that shows $0.00 posted as well as the $200 payment made that reduces the sales tax payable liability.