Confused by 100k personal allowance loss and tax payment request from HMRC.

Hi

I recently had a message from HMRC saying that I owe them tax as I earned over 100k in 23/24. My gross income for that period just reached 102k, but that doesn't seem to take into account the fact that I pay 12% of my gross wage into my employers pension. They contribute 9%. I don't know if i'm missing something here, but i thought that taking off the pension contribution would bring me in under the 100k and therefore protect my personal allowance. I have spoken to HMRC and they have said that everything seems good from their end and i should speak to my employer. I'm waiting on a response from them, but in the meantime was wondering if it could be the following

• Employer is not reporting correctly to HMRC, or
• Employer handles the tax deficit in PAYE so i won't be out of pocket, or
• I'm completely wrong and the tax is due.

Thanks