Please see this link for some solutions on validating your payment method.
If this message is coming up when trying to make your payment to the IRS, please see this link for more options available to you. If you have already electronically filed your tax return, you will not be able to make the changes within TurboTax. Instead, go to the Direct Pay help guide from the IRS for assistance. Scroll down to the section titled How do I...and select question 3 to verify your payment directly with the IRS.
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