Self Assessment and PAYE code adjustment

I am completing my 2022/23 SA to report BIK based on P11D from my employer. In July this year, I received a PAYE code adjustment letter for 2023/24 saying my 2023/24 PAYE code will be adjusted based on 2022/23 BIK figure from employer, and it also states that there is an estimated tax that I owed (this year), is this year refers to 2023/24 only? Is 2023/24 PAYE code adjustment only applies to additional 2023/24 tax due to the estimated BIK that I will be receiving for 2023/24 but nothing to do with the additional tax relating to my 2022/23 BIK? When filling in 2022/23 SA, what should I key in 'Underpaid tax included in PAYE coding' ? I couldn't find any figure on my 2022/23 PAYE coding letter with message 'our estimate of the underpayment for the earlier part of the year is GBPXXX'.

Hi,
 

As the code as been updated for 2023/24 and adjusted for an underpayment in the 2023/24 tax year then this will not be shown on the 2022/23 Self Assessment tax returnm .  Thank you.