High Income Child Benefit Charge - Underpaid tax and other debts and P800Hello, I am desperately trying to correctly complete the tax self assessment form of which I only have to fill in to pay High Income Child Benefit Charge (I am NOT self-employed). I have reached the 'Underpaid tax and other debts' section and have become a bit stuck ( a lot stuck tbh). It says: 'Amount of underpaid tax for earlier years included in your tax code for 2021-22 (from your PAYE Notice of Coding)' However I seem to have misplaced this exact form! I do however have a P800 from later in that year claiming I owe an extra £500+ in tax. This was paid from my wages but do I need to put this figure in the box or do I need to find out what the figure was in the original Tax Code Notice? The boxes were not pre-populated. Please help as I'm now on the final day to submit - the process is so complicated for someone who merely wants to pay back a minimal sum that may have been paid in child benefit. Many thanks.