Não está certo

You can use it as a standalone statement. If a waiter brings the wrong bill, just point and say it. You can also add que to explain further. For example, Não está certo que ele faça isso. This means "It isn't right that he does that." It is simple, punchy, and very effective. Don't worry about complex grammar here. The verb estar handles the temporary state of the error.

Use it at the office when a report has typos. Use it with friends when someone forgets their wallet again. It works perfectly in a restaurant if the steak is overcooked. It is great for texting when a plan seems unfair. If you feel a sense of "this isn't how it should be," say it. It is the verbal equivalent of a raised eyebrow.

Avoid it if you want to be extremely polite to a boss. In very formal settings, it might sound a bit blunt. Don't use it for permanent facts, like "The sky is not green." For that, you would use não é. Não está certo implies something happened that shouldn't have. It is about the situation, not the essence of the universe.

Brazilians and Portuguese people value social harmony but dislike unfairness. There is a strong sense of o que é justo (what is fair). This phrase is a mild way to protest without starting a fight. It is less aggressive than saying "You are lying." It focuses on the situation rather than the person. It is the polite person's weapon for justice.

You might hear Não tá certo in casual conversation. Brazilians love to shorten está to tá. If something is really wrong, add nada. Não está nada certo means "It is not right at all." For a more formal vibe, use Não é correto. But for daily life, the original is king.