Tax Refund in Error

PAYE Employee. 2 weeks ago I received a tax refund for Y/E 2024 that I claimed. My employer has now notified me that there was a problem with the M12 FPS file and so it was not submitted to HMRC. My taxable income for 2024 is now showing the correct figure on HMRC that matches my P60. How do I pay back the refund as presumably I’m not entitled to any of it? It amounts to around £350 and I would like to do it as a lump sum. Thank you in advance.

Hi,
You can pay this back via your personal tax account - Personal tax account: sign in or set up
Thank you.