This step only applies to some people. If none of it is relevant to you, you can leave it and your claim will still go through.
Where to find it
Sign in at app.taxpro.co.uk, open your claim, then open the Additional Info step.
The web address looks like app.taxpro.co.uk/claims/<your claim>/additional-info.
When you do need to complete it
You had income outside your PAYE job — self-employment, freelance or CIS work, rental income, or a pension.
You have a student loan being repaid through your pay.
You get benefits in kind from your employer, for example a company car, private medical cover or a fuel card.
You made pension contributions outside your workplace scheme, or gave to charity through Gift Aid.
You have investment or savings income worth declaring.
Why it matters
Where your claim goes through Self Assessment, the return covers your whole tax position for the year, not just your expenses. Leaving out other income can mean HMRC query the return later, which delays your refund. It is much quicker to declare it now.
Some of it works in your favour too. Pension contributions and Gift Aid can increase your refund.
If you're not sure
Tell us roughly what the income or benefit is and we'll tell you whether it needs declaring. Don't guess at figures, an approximate number you can't evidence is worse than asking.