Sales Tax Payable is the liability account that holds tax you've collected but not yet remitted, and it is the single account that must always reconcile to what you owe the state.
Every taxable sale credits this account; every remittance to a taxing agency debits it. Between filings, its balance is the running total of tax you're holding on the state's behalf. QuickBooks Online maintains this behind its sales tax center, and Desktop maintains it as a current liability tied to your sales tax items — but in both, the health of the account depends on tax flowing to it and nowhere else. Two habits corrupt it. The first is recording a sales tax remittance as an ordinary check or expense instead of as a sales tax payment; the money leaves the bank but the liability never clears, so the balance grows without end. The second is letting non-tax amounts, discounts, or journal entries land in the account, which breaks the tie between the balance and the returns you've filed. A Sales Tax Payable balance that agrees with your filed returns is proof the whole system is working; one that doesn't is the first symptom cleanup addresses.