If you did not have earnings before the conversion or any other pre-tax funds (balance was $0 on December 31, 2024) then the pro-rata rule won't apply and the conversion isn't taxable and line 4b of Form 1040 should be $0.
If this is not case please review your entries and my instructions above or these instructions: How do I enter a backdoor Roth IRA conversion?. Also, make sure you have the IRA/SEP/SIMPLE box checked when you entered the Form 1099-R.
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