If you are past the age for taking an RMD, and failed to do so, the penalty for 2023 is 25% of the amount of the missed RMD.
However, what you should do is request a withdrawal now (as soon as you can). When you file your tax return, you include form 5329 for the missed RMD penalty, but request a waiver of the penalty. (Part of the request for the waiver is that you took the withdrawal as soon as you realized the mistake in January.) These waivers are almost always granted.
Then, when it is getting close to the end of 2024, you will still need to take your RMD for 2024, since you are using the January 2024 withdrawal to count as your 2023 RMD. Make sure to set up the withdrawal a few days early, because it usually takes a few days for the broker to process the request, especially during the end of year rush and holidays.
Lastly, remember that an RMD is not a special transaction, it is the minimum amount you need to withdraw during the year. Suppose your RMD is $5000. That could be satisfied by a single withdrawal of $5000 on December 29, but it would also be satisfied if you had been withdrawing $500 per month all year for living expenses (since the total exceeds the minimum requirement).
If you had an agreement with the broker to make a withdrawal and the broker failed, I don't know if it is possible or practical to complain to the broker and have them pay the penalty for you. Your goal should be to request a waiver and not pay a penalty in the first place.
