Reporting part-time earnings while on benefits - any advice?

I picked up part-time shifts as a line cook and I am confused about how to report them. I do not usually post, so bear with me. The form asks for gross earnings, which I do not see until later. Did anyone get an overpayment notice from a mistake?

Thanks for writing this out. I went through something close to it last year, and it got easier once I kept a simple log of every call and form.

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