I have John Lewis dishwasher. It is rebranded AEG so I watched this video to figure out the fix
https://www.youtube.com/watch?v=5jgebTrf-ao&ab_channel=MikkoAuvinen
Basically if you unscrew bottom panel and you will see tray that its filled with dirty water. There is a buoy device that stops machine from working if it detects water in that tray. You just have to drain the water from the tray with the sponge and machine will start working. However, if this tray gets filled all the time that means that you have a leak somewhere that keeps filling in this tray.
Amer
September 2022