Self employment invoices & tax return

[Thingsthatgo]

I’ve just started a side hustle, and I’m earning a bit more than I thought I would. I am keen to stay under the £1k threshold for this tax year, to avoid a self assessment return, but will need to do one next year.
If I earn money but invoice later what date is relevant for tax reasons? The date I do the work, the date I invoice or the date I receive the payment?
Thank you for your help!

I go by date of invoice.

Simplified cash basis accounts - it is the date that you get the payment.

So looks like I can choose?