Formal:
* Pas important: This is the most literal translation and is generally appropriate in formal situations.
* Sans importance: This is another common and formal option, meaning "without importance".
Informal:
* Pas grave: This means "no big deal" or "it doesn't matter" and is more informal.
* Peu importe: This means "it doesn't matter" and is a versatile phrase used in both formal and informal settings.
* C'est pas grave: This is similar to "pas grave" but adds emphasis.
Other options:
* Ce n'est pas essentiel: This means "it's not essential" and is more formal.
* Ce n'est pas primordial: This means "it's not a priority" and is also more formal.
The best option for you will depend on the specific situation and your relationship with the person you are speaking to.