Told to restart self assessment

HMRC in 2021 messaged me to say I didn't need to submit self assessment any more. My state pension started in 2023. In 2023 they told me to restart self assessment but I didn't check my messages as I thought I no longer needed to submit returns. They have now given me a penalty for not submitting on time. Can you advise why I have had to restart? Is this because of the pension?

Hi Daveyworld,
It may be that your State Pension income exceeds the tax-free Personal Allowance.
Which would mean that we may only be able to collect any tax owed on that income via Self Assessment.
We would need more information to correctly advise you on this, though.
Please contact us by webchat or phone here:
Self Assessment: general enquiries
Thank you.