Okay; yet again let's look at what the dotGOV website says. Here you go - cut and pasted.
Adversely affected is typically when your business has experienced lower income or higher costs due to coronavirus.
HMRC expects you to make an honest assessment about whether your business has been adversely affected. There is no minimum threshold over which your business’ income or costs need to have changed.
If you make a claim for the Self-Employment Income Support Scheme grant you’ll have to:
keep records of how and when your business has been adversely affected
confirm to HMRC that your business has been adversely affected by coronavirus
And here's what the site says about the records you need to keep.
You should keep any evidence that your business has been adversely affected by coronavirus at the time you made your claim, such as:
business accounts showing a reduction in turnover or increase in expenditure
confirmation of any coronavirus-related business loans you have received
dates your business had to close due to lockdown restrictions
dates you or your staff were unable to work due to coronavirus symptoms, shielding or caring responsibilities
Published 17 August 2020