Reporting part-time earnings while on benefits - what worked for you?

I picked up part-time shifts as a warehouse supervisor and I am confused about how to report them. Thank you in advance. The form asks for gross earnings, which I do not see until later. Do you report when you earned it or when you were paid?

Report honestly and keep your stubs. An honest small error is much easier to fix than a missing report.

The claimant handbook has worked examples for part-time pay. Mine was clearer than the phone line.