Reduced Personal Allowance Not Showing On Self Assessment

Hi, I'm filling out my first Self Assessment and when I go to the "View Calculation" screen it is stating that my personal allowance for 23-24 was £12750. However during that year I received a letter from the HMRC saying that my personal allowance was being reduced and I finished the year with a Tax Code of 640L M1. This year I'm currently on 835L. The only reason I'm filling in a Tax return this year is that I went over 10K for interest earnings. I'm new to this but it appears the calculation for what I owe is based on me having the the full personal allowance available for PAYE but that wasn't the case. Am I getting this completely wrong? I thought the whole point in me having a reduced Personal Allowance was to proactively pay some of the additional tax. Thanks

Hi,
If your code was reduced to repay tax that you had underpaid in-year, in 23/24, then your full 12570 allowance showing in your 23/24 calculation is correct - the in-year reduction will effectively be present in the tax figure you enter as paid by end-of-year.
Your code may have been reduced for another reason, though - to allow us to check this, and confirm what needs to be entered in your return, contact us by webchat or phone
Self Assessment: general enquiries
Thank you.