Is it permissible to accept financial compensation of 150 euros from a tailor who ruined a suit, knowing that the original value of the suit was 250 euros, and it was purchased at a discounted price of 50 euros? Is this money lawful (halal) or unlawful (haram)? And what should be done if it is unlawful?

It is permissible to accept the financial compensation agreed upon with the tailor for his error in craftsmanship, regardless of the price paid or its current value. Conciliation is permissible among Muslims as long as it does not make a forbidden thing permissible or a permissible thing forbidden. It is also permissible to use the suit as long as you have been given permission to benefit from it.