For 2024, to avoid penalty you need to pay during the year, thru withholding or timely (usually quarterly) estimated taxes (ES), the smaller of either: 100% of your 2023 tax (110% if AGI > 150k) or 90% of your 2024 tax, this is your 'safe harbor' amount.
If the additional income increased your safe harbor amount such that the withholding you usually make was insufficient to meet it, then you needed to have paid ES for that difference. And the ES needs to either be paid quarterly, by default the IRS assumes your income is earned evenly thru the year, withholding is assumed to be paid evenly also, but ES need to be paid quarterly to be considered 'timely'. Even if you pay the balance when you file, the penalty is assessed quarterly and you need to 'pay as you go' to at least meet your safe harbor amount prior to filing.
Alternatively, you can make a one-off ES payment for one-off income and file Form 2210 'annualized income' method to show how the ES payment lined up with uneven income, this is particularly useful for unplanned income events later in the year e.g. Roth conversions - and may fit your situation.
That said, when you prepared your return, TT should have calculated a penalty and given you the opportunity to adopt the annualized income method to minimize that penalty (Other Tax Situations / Underpayment Penalty). If you are on TT desktop you can double-click in Forms mode on Form 1040 line 38 and again on the worksheet to bring up the Form 2210 calculations.
So if you paid what TT prepared on Form 1040 which includes the penalty, but IRS came back with a penalty notice that could mean some information is different between the IRS and what was input into TT, as the IRS independently calculates it based on data in their systems. If you didn't have the correct 2023 AGI/Tax information in TT when you prepared 2024 then TT may have assessed no penalty was due based on a lower safe harbor amount than the amount determined by the IRS.
I would start by determining yourself whether or not a penalty was due (see Form 2210 lines 1-9) based, and if so why TT didn't calculate one.
At a minimum you may be able to adopt the annualized income method to reduce the penalty (I'm not sure the process for doing this after filing - see if the CP30 has guidance or others may weigh in here).
More info on ES https://www.irs.gov/faqs/estimated-tax
More info on Form 2210 https://www.irs.gov/pub/irs-pdf/i2210.pdf
Not a CPA just a few thoughts based on what you described, hope this helps.
