All trades are solved at the same time for the next 24h day in a single algorithm run for all Europe at 12h and taking about 15min to solve. You notice at the end and if it converge they won't re-run it for you, it's done.

Many probably did. But as a buyer/reseller it would be in their best interest to just buy and shut up.

… Wait, how do you think modern markets _work_? Hint: it is not an elderly man writing numbers on a ledger with a quill pen. There is not generally a human in the loop.

Other regulated commodity markets have what is called a «reasonability limit» avoid this exact kind of scenario. It is very concerning that the exchange didnt have any automated alerts that could trigger for example a phone call to verify that the order is correct.

The limits are there. -500€/MWh and 4000€/MWh. It did hit the lower limit for 10 hours in the row from 14:00 till midnight. Before 14:00 they were not the last bidder, so prices are higher there. Price on the market for everyone is set by the last bidder who fits in the predicted consumption pool.

They have price limits, but I think GP means volume alert limits. Someone unexpectedly bids a third of the Finnish production capacity, you call them and ask if they are sure.

Nor a suitable test suite to catch this kind of thing preëmptively.