Confirm the area of the leak first, watch it fill. There is a large nut on the inside holding the air break, also a clip on the air break to water softener, then it lifts off to access o rings.The two black o rings are visible in your picture.
Being made by Smeg, the usual leak is the two o rings, air break to water softener, to the left and slightly above your red circle.
Watch it filling to confirm, it runs down to the area you have marked.
Take the left hand side panel off and watch it fill. Most common culprit are the o rings air break to water softener.
Anti flood should have kicked in before reaching the pumps.
You can flush it down with a garden hose, it's a two man job with someone turning the tap on slowly to start with in case it backs up.
Put the machine on a rinse afterwards empty, then check the filter for any lint.
I would have a close look at the lower spray arm, sometimes they come apart at the sides pushing a jet of water sideways which breaches the lower door seal.
You can test the heat pump in situ.Remove the six lower door panel torx 20 screws, then pull the panel away.Unclip the lower plastic kick strip.
Then two more t20 screws on the lower panel. The heat pump is to the right, the connector with an earth connection and two red wires is the one to...