Paye Notice of Coding vs tax code notice for self-assessment

My question might be similar to one posted here a few months ago regarding PAYE Coding Notice - that thread was helpful for me, but only up to a certain point. I'm filling in my tax return for my small freelancing business and this is the very first time for me. I got to the question: 'Amount of underpaid tax for earlier years included in your tax code for 2021-22 (from your PAYE Notice of Coding). Please enter '0' if there is nothing shown' I don't have any PAYE Notices of Coding to view on my account and the last time I received one was 2014 and it does not have any information about underpaid tax. This is the explanation I see for the lack of PAYE Notice of Coding on my account: 'You may not be able to view your PAYE Coding Notices if either of the following apply: - you or your agent were not registered for Self Assessment Online when the Coding Notice was issued - no PAYE Coding Notices have been issued since 10 October 2011.' I believe the first option applies to me. I have received my tax code notice for the year 2021-2022, but there is no mention of underpaid tax, even with the amount of 0.00. I did owe tax the year before (but it has been paid since then) and my tax code notice for the year 2020-2021 did show the amount owed. Now my questions are what can I do to progress with the filling of my tax return? Can I use my tax code notice for 2021-2022 and type 0.00 even though that notice does not include this information or do I really need my PAYE Notice of Coding for that year? What can I do if I have not received it and can't view it on my business tax or PAYE tax account? Thank you in advance for your help.

Hi,

If there is no mention of underpaid tax in the notice that you have, you should enter 0.00.

Thank you.