Reporting part-time earnings while on benefits, bank teller here

I picked up part-time shifts as a bank teller and I am confused about how to report them. I have been trying to stay organised about it. 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 7 months ago, and it settled down once I kept a simple log of every call and form.