Bonus Paid in following tax year.

I retired in Sept 2023, and was on the 40% tax bracket for 23/24 tax year. This month the company I did work for paid me a pro-rata payment of a bonus ( April 23 to Sept23) this month (may 2024). my question is do I pay tax on that payment at 40% ( from the 23/24 year) or at my new tax code as a retired senior citizen ( which is no where near 40%. thanks

Hi ste western,
It will be at the rate you are liable for in 24/25.
Thank you.