In some countries, rather than sending you a bill, the government calculates what you owe and then refuses to tell you. You are then responsible for working out the same solution they did and then paying them (note that both steps are hard, and the government may refuse payment without explanation).

If you successfully pay them and the payment was too low, they may come after you, typically with fines, but if you fucked up badly enough, potentially even jail time. Same thing if you did not succeed in paying them at all, because that will count as failure to file even though it’s their fault.

If you overpay, the government chuckles and pockets the difference.