PAYE underpayment

I have received a police pension for 14 years. In June 2022 I commenced a part time job with another public body. My tax payment for 2022-2023 is shown as correct. I've just received notification that for 2023-2024 I have and underpayment of £1000. Nothing changed in my circumstances during the 2 year period. This is PAYE , how does this happen. Could it be a mistake.

Hi Druinnes,
In this circumstance it may better for you to contact ourselves.
Please see link here, as we will need to access your record and this forum can only answer questions of a general nature.
Income Tax: general enquiries
Thank you. 
 

I have received a notification of an under payment on my PAYE Tax and was wondering is there a way to pay it back in a lump sum??

Hi Curtis,
The notification you received should have information on how to repay the underpayment. This could be either online via your Personal Tax Account, or using a cheque and a payslip.
Thank you.

My underpayment was notified with a change of tax code only. In this situation is it possible for me to pay the underpayment payment to HMRC in a lump sum?

Hi,
You can make a voluntary payment to pay the underpayment in full. If you contact our Income Tax team they will discuss the payment options available which is dependant on the information held on your tax records.
Income Tax: general enquiries
Thank you.