Reporting part-time earnings while on benefits after 15 years as a software tester

I picked up part-time shifts as a software tester and I am confused about how to report them. Pay posts on a different day from when I work. 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.

I estimated and then checked my pay stub. When there was a small difference I wrote to the agency to correct it.