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

I picked up part-time shifts as a copywriter and I am confused about how to report them. I have read a lot of threads here and could not find my exact situation. Pay posts on a different day from when I work. 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.