Second IRS charge after filing

Hi,

Realizing after the fact that I had a second charge direct to the IRS after filing my federal return. I had additional taxes due, but no known penalty as most of the tax bill was due to some Roth conversions I decided to make. Total value is $48... far under what I ultimately owed. Any ideas of what this is for? I looked at the IRS site directly and did not find any additional details that would explain this. The description clearly states its a direct charge to IRS, not a separate Intuit or TurboTax filing fee.

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