2022-2023 calculation of Self assessment on rental income including PAYE figure

Hi, I have single employment earning (PAYE) £33700 annum. And one residential rental property (rental income 12k in 2022-2023), which is split 50-50 with a partner (rental income £6k each) and expense of £1000. No other income. After my self assessment, I have noticed income tax calculated again on my employment income giving almost £1400 tax due for year 22-23. This cannot be right. PLease help Thanks What am i doing wrong?

Hi fleeting glimpse,
The tax is based on the total income received and you will be due to pay 20% on the rental income.
The additional tax due may be due to other items claimed/not claimed in the return but were in your tax code.
Thank you.