Schedule 3 line 15 is a total. Do you have an amount on Sch 3 line 10? That is a payment made with an extension to file. Find it here......
Federal Taxes (or Personal for desktop H&B version)
Deductions and Credits
Then scroll way down to Estimates and Other Taxes Paid
Other Income Taxes - Click the Start or Update button
Next page second section Payments with Extension
Either Visit All or Click Start or Update by the extension to delete the amount
If it's not there then we need to know what line 9-13 on schedule 3.
