High tax deducted upon changing tax code

I'm unsure how the tax code 2288L was automatically assigned by HMRC. I moved to a new job in June 2023, and my tax code last year was BR (Basic Rate). Recently, I changed my tax code from 2288L to 1257L in August 2024 after receiving an email from HMRC in late May 2024. After updating my tax code to 1257L, I noticed a 40% tax deduction from my August 2024 salary. Could you help me understand how this was calculated? Did I make an error in updating my tax code to 1257L?

Hi,
In order to check your tax code is correct you will need to contact HMRC directly: Income Tax: general enquiries
Thank you.