You can pay on the IRS site.
https://www.irs.gov/payments
When you requested your extension you were supposed to pay your estimated tax due. Did you enter the payment you made into your tax return? Go to Federal>Deductions and Credits>Estimates and Other Taxes Paid>Other Income Taxes
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
