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

I picked up part-time shifts as a customer-service rep and I am confused about how to report them. There are 10 people counting on me, so I am trying to be careful. The form asks for gross earnings, which I do not see until later. Did anyone get an overpayment notice from a mistake?

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