Thanks for the responses. Yes, it does look like I can submit the self assessment return even though it has a warning and alert showing. The "loss brought forward" figure I've inserted is showing as an income tax relief in the final calculations, as I'd expect.
I have one employment and one self employment. The self employment made losses in years 17/18,18/19 and 19/20 but a profit in 20/21 and this year 21/22. I'm trying to put a figure in the self assessment online form for "Loss brought forward from earlier years set-off against 2021-22 profits: (optional)" of 1245, which is equal to the "Net business profit for tax purposes:" amount shown just above that box. I'm unable to do so, because the page keeps generating a red warning "IMPORTANT: Please check the help on the 'Loss brought forward' field and review the figure entered in this box".
When I check that help "Help about: Self Employed short 34 - Loss brought forward from earlier years set-off against 6 April 2021 to 5 April 2022 profits" it just says "Include the amount of any losses you sustained in this business in the tax year 6 April 2020 to 5 April 2021 and earlier years which you have not yet used, to be set-off against the 6 April 2021 to 5 April 2022 profits." That is what I am already doing.
Why is the figure I'm entering in this box deemed incorrect?
Is there something I need to do elsewhere in the Self Assessment online form to confirm that I still have unused losses from three previous years that I want to offset against profit from this year?