No, the IRS doesn't void your extension and charge you a failure to file penalty, as long as that extension is filed on time.
You will be charged for failing to pay on time, underpayment penalties, and interest on the unpaid balance.
Technically, there's a penalty for understating your tax liability by more than 20%, but that is applied to filed returns, not extensions. Even so, I'd be cautious about intentionally underpaying your extension payment.
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