Reporting part-time earnings while on benefits - 16 weeks in

I picked up part-time shifts as a social media manager and I am confused about how to report them. It has been a long 16 weeks. 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.